GIS Glossary Part 2- Paritosh, the Geo-soldier
L
label
(CAD context) A CAD element that contains text used to identify a point,
line or polygon element.
label
(vector context) Text in a vector object used to identify a point, line,
or polygon element.
label
(window context) The static text part of a component that presents
information to the user about that component, such as the action invoked by
a push button or the mode selected by a check button.
labeling
(raster context) Identifying and grouping the clusters that result from
any kind of automated image interpretation. You choose labels (names for
types of features) based upon your knowledge of the areas or materials in
the image.
LAI
See - leaf area index.
land cover
The materials that cover a study site, such as vegetation, bare soil,
rock, sand, and water.
Landsat satellite
A satellite that collects multispectral images. At various times it uses
1) a Return Beam Vidicon (RBV) device, 2) the Multispectral Scanning (MSS)
device, and 3) the Thematic Mapping (TM) scanning device. Landsat also
relays data from ground observation stations. Landsat was originally called
the ERTS or Earth Resource Technology Satellite.
LAS
A raster-based, public domain image processing system.
lateral connections
HyperIndex connections between objects on the same hierarchical level.
The connections may be individually established by the user or automatically
estimated. HyperIndex displays a list of laterally connected objects when a
user indicates a move in that direction with the arrow key.
Latin alphabet
The character encoding scheme used by most Western nations, based on the
alphabet developed in Roman antiquity, itself a derivative of the Greek and
Western Semitic alphabets. The Latin alphabet is used by the languages of
Western Europe, including English, as well as many other languages such as
Turkish, Swahili, and Vietnamese. The Latin alphabet is sometimes referred
to as the Roman alphabet, but "Roman" is not used in this
discussion so as to avoid confusion, since the term "Roman" is
often used in typeface and character style contexts.
Latin-1
(also known as ISO 8859-1) A super set of the 7-bit ASCII character
encoding scheme that includes various symbols plus letters with diacritics
commonly used in European languages. Latin-1 is an 8-bit character encoding
scheme, containing 256 characters. Latin-1 makes different assignments for
codes 128-255 than does PC-8. Latin-1 is, however, consistent with the
Unicode and ISO 10646 standards, and is the common encoding scheme used by
Unix systems.
latitude
The angular distance in degrees of a point on the earth north or south
of the equator.
Lattice
A surface representation that uses a rectangular array of mesh points spaced
at a constant sampling interval in the X and Y directons relative to common
origin, A lattice is stored as a grid, but represents the value of the
surface only at the mesh points rather then the value of the centre cell.
layer
A display entity comprised of one or more components that can be
manipulated separately from other layers. There is often a one-to-one
correspondence between layers and objects, but an individual layer may be
comprised of multiple objects, such as the red, green, and blue components
used to create a single layer in multiple raster display.
leaf area index or LAI
A unit-less, biological measure equal to the ratio of the one-sided
surface area of the leaves in an in situ crop, forest, or grassland canopy
to the ground area.
least squares
A mathematical method for fitting a line or curve to a set of data
points. Least squares minimizes the sum of the squares of the error term at
each point.
Lengend
1. The reference area on a map that lists and explains the colors, symbols,
line patterns, shadings and annotation used on the map. The legend often
includes the scale, origin, orientation and other map information.
2. The symbol key used to interpret a map.
level
In HyperIndex, any object or file that is displayed in the Display /
Spatial Data window is called a level. A level may originate from a raster,
vector, or CAD object. However, in HyperIndex, the level assumes an identity
beyond that of the object or file itself, because the level includes the
index areas that have been defined and any links to other objects. Thus, in
addition to being an image, a level lets you access many different kinds of
information. (See also: HyperIndex, index area, link, stack.)
limit line
An adjustable graphic line on a process control screen that defines the
boundary between values that are used and values that are not used in the
process.
line
(raster) One horizontal row of cells (or pixels) in a raster object (or
display image).
linear contrast
See - contrast.
Linear feature
A geographic feature that can be represented by a line or set of lines. For
example, rivers, roads within a pizza delivery area, and electric and
telecommunication networks are all linear feature.
linear transform
(map registration) One kind of map registration subobject (Regist) that
contains an object's mathematical representation for its calibration
solution (least squares) derived from a control point list.
line element
One of the types of elements which make up a vector object. A line is
defined by an ordered string of coordinates which define a curved path in
space. Line attributes include-
| attribute |
|
example |
|
| ID
number |
|
a
unique reference number |
|
| class |
|
intermittent
stream |
|
| group
number |
|
hydrology |
|
| color |
|
RGB
line color |
|
| database
record no. |
|
pointer
to record |
|
| line
pattern |
|
slashes
on line |
|
| line
width |
|
thickness |
|
Vector element class attributes may be cross-indexed to a list containing
the database record, polygon fill pattern, line drawing pattern, point
symbol, line width or symbol/point size, RGB color, RGB label color, RGB
fill color, label font number, label font size, label font zoom factor,
label font style, and label rotation angle.
Line-in-polygon
A spatial operation in which arcs in one coverage are overlaid with polygons
in another to determine which arcs, or portions of arcs, are contained
within the polygon attributes are associated with the corresponding arcs in
the resulting line coverage.
line pattern
The drawing style of a line for display or printing
link
(to external database or raster object). A project file link to an
external database file contains the file name, device location, and
field/record information about the database file.
link
(HyperIndex). The relational connection between a region (or index area)
on a parent object and daughter object in a HyperIndex stack
list box
A scrollable list of options from which to choose.
local variable
(SML) Variables that belong to a function or procedure and exist only
for that procedure are "local variables." No variable is local
unless it has been explicitly designated so with the "local"
statement in the function or procedure. A local variable may have the same
name as a variable used elsewhere in the program without affecting it.
locale
One collection of data that defines the semantics for a specific
language and set of cultural conventions. Standard C provides a Locale
structure which includes six aspects of the local culture and language: 1)
Collation / sort sequence for characters, 2) Character type, 3) Money and
currency symbols and formats, 4) Numerical formats: a point or comma for
decimal demarcation, 5) Time - names of the weekdays, 6) Messages - yes/no,
program status and prompts.
localization
Providing the run-time data that describes the necessary elements of a
locale for an internationalized program so it can use the correct character
encoding scheme, font, keyboard conventions, collation sequence for the
alphabet, and so on.
Logical Connector
One of the reserved words AND, OR and XOR used to build complex logical
expression in query.
Logical operator
Another term for Boolean operator.
Log file
A coverage or workspace history file containing a list of all commands used
to operate on a coverage or all commands used in the work space.
Logical expression
A combination of items, system items, system variables, literals and
arithmetic logical operators from which a value of TRUE or FALSE is derived;
for eg. $RECNO LE$NUMI HRS - WORK * HRLY- WAGE GE 600 AND $ MONTHEQ 5 $NOMILE
100
longitude
The angular distance in degrees of a point on the earth east or west of
the Prime Meridian.
low-pass filter
A process that smoothes or reduces the spatial variability or detail in
a continuously varying raster object. (See also: filtering)
M
Macro
A text file containing a sequence of commands that can be executed as one
command. Macros can be build to perform frequently used, as well as complex
operations. The ARC Macro Language (AML) is used to creat Mocros for
ARC/INFO
Map
An abstract representation of the physical features of a portion of the
Earth's surface graphically displayed on a planar surface. Maps display
signs, symbols and spatial relationship among the features. They typically
emphasize, generalize and omit certain features from the display to meet
design objectives. (eg railroad features might be included in transportation
map but omitted from a highway map.)
Map Generalisation
The process of reducing details on a map as a consequence of reducing the
map scale. The process can be semi - automated for certain kinds of data,
such as topographical features, but requires more insight of the thematic
maps.
mapping unit
See - soil mapping unit
map projection
"A device for representing all or part of a rounded surface on a
flat sheet. Since this cannot be done without distortion, the cartographer
must choose the map characteristic (area, shape, scale, direction) which is
to be shown accurately at the expense of others." Map Projections Used
by the U. S. Geological Survey, Geological Survey Bulletin 1532, Second
Edition, U. S. Government Printing Office, Washington, D.C., 1982, p. 5. The
map projection geometrically or mathematically generates the grid of lines
of latitude and longitude.
Every process that establishes or translates map projections offers the same
standard selection list of projections. The practical choice of map
projections for ungeoreferenced project materials is normally determined by
the kind of projection used by those project materials that are calibrated
to a projection. For example, if you have a scanned USGS topo map in the
polyconic projection, you may decide to calibrate (or translate existing
calibration) satellite images and vector overlays to the same projection.
(See also: ellipsoid.)
map quadrangle or map quad
The geographic area covered by a map. One kind of map quadrangle is the
7.5' x 7.5' area that is covered by a standard USGS 7.5' topographic map.
Referring to a 7.5' map quadrangle does not imply the presence of an actual
paper map. The term may simply designate the area covered by electronically
stored materials.
Map query
The process of selecting information from a GIS by asking spatial or logical
questions of the geographic data. Spatial query is the process of selecting
features based on location or spatial relationship (eg select all features
with 300 feet of another, point a set of feature to select there). Logical
query is the process of selecting features whose attributes meet specific
logical criteria (eg, select all polygons whose value for area is greater
than 10,000 or select all streets whose name is main st.') Once selected
additional operation can be performed, such as clearing them, listing their
attributes or summarizing attribute values.
map scale
The relationship that exists between a distance on a map and the
corresponding distance on the earth. It may be expressed as an equivalence,
one inch equals 16 statute miles; as a fraction or ratio, 1:1,000,000; or as
a bar graph subdivided to show the distance that each of its parts
represents on the earth.
marking features
Saving prototype areas that have been classified in feature mapping,
clustering, or some other interpretation process as permanent features.
Marked features can be unmarked. (See also: labeling)
mask or data mask
A processing barrier or boundary that only allows selected data values
(perhaps in a chosen range or area) to pass. Users might choose a data mask
that blocks all values outside a selected value range, eliminating all image
features except those in the range they want to use in a process. A mask is
more often used to confine the effects of a process to a selected area of a
raster object. (See also: processing mask.)
maximum-likelihood classification
A supervised image processing routine usually applied to multivariable
images that have a dimensionality greater than 3. First, the user selects
sample areas, (called prototype or training set areas) for each feature to
be mapped. The maximum-likelihood process then computes the statistical
properties of these features. Similarly, it determines the statistical
characteristics which separate feature types. After this identification
model has been built, the process tests each cell to determine in which
prototype group it most probably belongs. A threshold can be set so that if
the highest probability of a feature match is below the threshold, the cell
is designated as unknown. This "catch-all" group insures that a
cell representing a feature type not defined in one of the training sets
will not be forced into membership.
MCA
Micro Channel Architecture. The bus architecture used for IBM PS/2 Micro
Channel machines.
megabyte, Mbyte, or MB
A unit of measurement for (approximately) 1,000,000 bytes, 1,000
kilobytes, .001 gigabytes, or .000001 terabytes. (See also: bit, byte,
exabyte, gigabyte, kilobyte, pecabyte, terabyte.)
menu
A pulldown or popup list of selection options.
menu bar
A graphic component at the top of a window that displays the titles of
the pulldown menus.
meridian
A great circle on the earth's surface that passes through the
terrestrial poles.
message box
A type of dialog box that contains a message or warning provoked by a
user request or processing condition. The user must respond (for example by
selecting the OK push button) before the interrupted process can resume.
MI
MicroImages, Inc.
MICROPIPS
A raster-based microcomputer image processing system developed and
distributed by the Telesys Group, Inc. This inexpensive entry-level system
runs on standard color display cards such as the CGA and EGA and uses a
menu-driven interface. MICROPIPS is a well-documented choice for users who
want a good training vehicle.
MIDI
Musical Instrument Digital Interface.
minimum distribution angle
An unsupervised classification or clustering process developed by Dr.
Jack Paris and presented in: Jack F. Paris and Helenann H. Kwong (1988)
Photogrammetric Engineering and Remote Sensing 54(8):1187-1193.
Characterization of Vegetation with Combined Thematic Mapper (TM) and
Shuttle Imaging Radar (SIR-B) Image Data.
min/max box
A rectangle that encloses a vector or CAD element such that the edges of
the box indicate a minimum or maximum coordinate value for that element.
minute or '
"The sixtieth part of a degree of angular measurement, often
represented by the sign ' as in 12° 30', read 12 degrees, 30 minutes"
(Random House). USGS quadrangle maps are common in both 15 and 7.5 minute
sizes. For example, the 7.5 minute map for Crow Butte, Nebraska covers from
103° 15' to 103° 22' 30" west, and 42° 37' 30" to 42° 45'
north. (See also: arcsecond, degree.)
mnemonic
A single keyboard character associated with a labeled component (such as
a push button or menu selection). The mnemonic is underlined in the label,
or if the mnemonic is not contained in the label, it can follow the label in
parentheses. The underscore in the menu selection "View", for
example, indicates that the letter "V" is the mnemonic for that
selection, and that pressing the "V" key on the keyboard will
activate the View selection. (See also: accelerator.)
model area
The area of overlap in a pair of stereo images that is selected for
creation of a DEM.
monochrome image
An image displayed in a single color or shades of a single color. Most
monochrome computer displays use white, green, or amber, although it could
be any one color.
montage
A process in the Mosaic process that assembles individual images into a
single raster object without regard for geographic or other inherent spatial
relationships. Tiling is a similar process, but assumes that the objects to
be assembled have parallel grids and equal scales, and so may be accurately
joined. (See also: mosaic, tiling)
mosaic
A large image assembled from segments. Each segment may come from a
different source and have a different cell size and angle of orientation,
but all the segments must be geometrically rectified and calibrated to a
common coordinate framework. The mosaic process rotates and re-scales each
piece and creates a single combined object. If all segments are
georeferenced to the same map projection, they can be automatically
mosaicked based upon their geographic calibration without additional
adjustments. Recognized verbal forms of mosaic are mosaic, mosaicked and
mosaicking. Montaging and tiling do not re-scale or rotate image segments.
(See also: montage, tiling.)
MOSS
Map Overlay and Statistical System. A pioneer vector-based geographic
information system (GIS) developed and still widely used by groups in the
USDI, especially the USF&WS and BLM. MOSS vector data files contain
strings of coordinate pairs which describe closed polygonal areas, lines,
and single point features. Common boundaries between adjacent polygons are
repeated twice in this data structure, once with each polygon. Much
geographic data is available in this format, especially that portion of the
NWI wetland maps which have been digitized.
motherboard
The main circuit board in a microcomputer. The motherboard normally
contains the main processor, logic chips, memory, and expansion slots for
optional circuit cards.
mouse
A computer graphics pointing device. As you move a mouse across the
desktop, the mouse cursor moves across the image display.
mouse cursor
Shows the position of mouse activity or focus on the screen. The mouse
cursor changes shapes to show the function currently assigned to the mouse.
For example, an arrow pointer indicates that the mouse may be used for
selection. An hourglass or clock shape shows that the mouse is inactive
during a processing activity.
mouse pointer
See - mouse cursor
MRI
Magnetic Resonance Imaging. A technique used in medicine to collect
computer images of internal organs and systems for examination and
evaluation. A device used in medicine.
ms (millisecond)
One thousandth of a second. A measure of average disk access time (the
time it takes the drive to position the read/write head over the requested
track).
MSS
Multi-Spectral Scanner. A sensing device on the Landsat satellite that
collects simultaneous images over multiple ranges of the spectrum.
multi-byte strings
Text in some character encoding schemes exceeds the 256-character
limitation of single byte encoding. In multi-byte systems, characters are
allotted 2 or 4 bytes each.
multilingual application
A computer program that allows the user to mix multiple languages and
character sets is said to be multilingual such as a word processor that
allows side-by-side columns of English and Japanese, or even mixture of
Latin characters within a longer Japanese text. Multilingualization is more
complex than internationalization, which limits the program to one local
language at a time.
multiple raster set
A set of coextensive raster objects displayed in unison. When the
multiple raster display mode is RGB, HIS, or HBS, three objects are included
in the set. When the multiple raster display mode is RGBI or RGBB, four
objects are included. One object in the set is assigned to each display
component.
multisensor images
Coregistered images with the same cell size collected by different
sensing devices. For example, a 10-meter SPOT panchromatic image can be
coregistered with a resampled Landsat TM image so that their cells correctly
match. This combination is called a multisensor image.
multispectral images
Images optically acquired in more than one spectral or wavelength
interval. Each individual image is usually of the same physical area and
scale but of a different spectral band. The MSS and TM sensors aboard the
Landsat satellite both collect simultaneous multispectral images. The TM
sensor scans and stores seven individual images in spectral bands ranging
from the blue wavelengths up to those in the thermal infrared.
multitemporal images
Coregistered images collected at different times by the same device. For
example, airvideo images collected one year apart, digitized, and warped to
the same geometry are called multitemporal images and can be analyzed to map
the changes between the dates.
multivariable images
An image stored on more than one independent, coregistered raster. For
example, a video framegrabbed image stored as independent red, green, and
blue rasters is a multivariable image. So too is any multitemporal,
multispectral, or multisensor image.
N
NAPP airphotos
National Aerial Photography Program airphotos. USGS CIR high altitude
airphotos. The NAPP series replaces the NHAP series. (See also: NHAP
airphotos)
NASA
National Aeronautics and Space Administration.
NAT
Node Attribute Table. A table containing attributes for node coverage
features. For each node, the NAT contains a reference to one of the arc it
connects to, an internal node sequence number and node feature identifier.
navigation
Moving a selection highlight or location cursor with a mouse or keyboard
through the levels of a menu and window system.
ND, ND6 and ND7
Normalized Difference. Vegetation index computations developed for use
with Landsat MSS. These vegetation indices are now commonly used with any
image that has the required spectral bands. The bands required are
approximately equivalent to the red and the photo-infrared spectral bands
measured by color-infrared film. The ND6 index used MSS band 6, and ND7 uses
band 7. Since these two Landsat MSS infrared bands are so highly correlated,
similar results are possible using either of the computations or with any
images that have an equivalent photo-infrared spectral band. Good
color-infrared image sources for processing into an ND or green biomass
raster include Landsat MSS and TM, SPOT CIR, 35mm CIR film, 9" CIR
film, and CIR video.
nearest neighbor sampling/interpolation
Resampling a source raster to yield a new raster with a different cell
size, raster orientation, and/or internal geometry by computing the distance
between the center of each cell in the output raster and the 4 nearest cells
in the input raster. The data value for the closest input cell is assigned
without alteration to be the data value of the output cell. Therefore, the
input value of one input cell may be assigned to more than one output cell.
It also means that some input cells may not be transferred at all to the
output raster. These undersampling and oversampling situations occur when
the cell sizes of the input and output raster are different.
For example, a resampled output raster which is coparallel to the input
raster but which has cells half as big, will repeat the input values in a 2
x 2 cell pattern. However, since nearest neighbor resampling does not
mathematically compute the new cell's value, it is the only suitable choice
for rasters that are not mathematically continuous such as land cover maps.
With such maps, mathematical resampling (like bilinear, or cubic
convolution) is totally incorrect since mean values cannot be computed.
Network
1. An inter connected set of arcs representing possible paths for the
movement of resources from one location to another.
2. A coverage representing linear features containing arcs or a route
system. Also known as network coverage.
3. When referring to computer hardware systems, a local area network (LAN)
or a wide area network.
NETWORK
The ARC/INFO software product that performs address matching/geocoding,
allocation, renting and pathfinding across linear networks.
NHAP airphotos
National High Altitude Program. NHAP is underwritten by the USGS and
provides a publicly available collection of CIR airphotos covering the
United States in print or transparency format.
nibble
A data element made up of 4 bits and having 16 possible values. Nibbles
are stored two to a byte.
NOAA
National Oceanographic and Atmospheric Administration.
Node
1. The beginning and ending location of an arc. A node is topologically
linked to all arcs that meet at the node.
2. In Graph theory, the location at which three or more lines connect.
3. The three cornered point of each triangle in a tin. Every sample points
input to a tin becomes a node in the triangulation. A triangle node is
topologically linked to all triangles that meet at the node.
node element
A vector element required for topology that has no attributes except
position; nodes occur at the ends of all lines and at all line
intersections.
nominal image map
A preliminary map form that approximates an image map and that can
usually be prepared using fully automated procedures. (See also: image map.)
non-interlaced video
Video signal formats used in some new display boards and monitors. A
non-interlaced video display board refreshes the whole display every 1/60 of
a second. It does not intersplice fields but paints each successive line
from top to bottom of the screen. Since the line refresh is twice as fast as
standard video technology, the picture and lines do not noticeably decay
between frames. Non-interlaced video is not standard, so if non-interlaced
technology is chosen, extra care must be taken to match the monitor and the
display board.
normalized contrast
See - contrast.
Normalized Difference
See - ND
normalized histogram
A histogram whose distribution has been adjusted so as to have as close
to a normalized (bell-shaped) distribution as possible. The data value that
occurs most frequently will be near the center of the histogram. Multimodal
histograms are those which have two or more significant peaks in their
distribution and cannot usually be satisfactorily normalized.
northing
A rectangular (x,y) coordinate measurement of distance north from an
east-west reference line, usually the equator or other parallel used as the
axis of origin for a map zone or projection. False northing is an adjustment
constant added to coordinate values to eliminate negative numbers.
NTSC video
National Television Standards Committee video. The standard format used
by all American home video equipment (like VCR recorders and television
sets). All the necessary color information is encoded in a single interlaced
signal which is often called composite color video.
NWI
National Wetlands Inventory conducted by the USF&WS.
O
object
An integrated, organized unit of data stored either in a project file.
These include raster, vector, database, and text object types.
opaque color
When a new color feature completely masks out an earlier feature in an
image, the new feature is composed of opaque color. For example, a polygon can
be overlaid or drawn in opaque color upon an image so as to completely
obliterate the original features in that portion of the image.
open reel tape
Medical images and satellite images from mainframe and minicomputers are
commonly distributed on 12-inch reels of magnetic tape in standard format. A
microcomputer with a open reel tape drive can copy image files directly from
tape.
operand
A parameter that designates a raster object's identification and location
in a raster algebra expression.
operator
The function in a raster algebra expression that describes action upon a
raster object or the process by which raster objects, or operands, are to be
combined.
optical disk
A high-capacity medium for computer file storage that uses removable
optical disk cartridges that function like removable hard disks. Each side of
a two-sided optical disk typically holds from 300 to 500 megabytes of data.
Some optical disks (WORM disks) record data permanently: once data has been
written on a WORM disk it cannot be erased or changed. More recently, erasable
optical disks have been developed. (See also: erasable optical disk, WORM
drive.)
optimization table
The translation table that determines the color assignment in the color
map that results from the optimization process. Optimization tables are used
to assign display colors for multiple raster display in 8-bit contexts.
option
An item on a menu. Also called a selection.
option button
A type of button that opens an option menu. When a new selection is chosen
from the option menu, the new selection is displayed as the button label.
ORACLE
A relational database Management System to which ARC/INFO has access through
the DATABASE INTEGRATOR
origin (X-Y digitizer)
The point on an X-Y digitizer's active area which has the coordinates
(0,0). The origin is typically located in the lower left corner of the active
area, but can be relocated in many digitizer models.
orthoimage
An airphoto or satellite image that has been processed to remove
perspective distortions and so to have the properties of an orthographic
projection. Distortions of tilt and relief are removed so that all features in
an orthoimage are in their true orthographic positions.
ortho photo
An airphoto that has been scanned, rectified, and reconstructed so as to
represent its features in a map projection or at least in a flat rectangular
form without the usual distortions of geometry and perspective. Usually
orthophotos are prepared from very high resolution stereo pairs.
ortho video
Airvideo images always include some geometric distortion from the camera,
lens, movement and perspective. Orthovideo images have been geometrically
corrected with control points from a corresponding vector object. The control
points are used to rubbersheet or warp the airvideo frame to yield a new
raster with more map-like geometric properties.
outline font
A font in which each character is described by a set of lines or polygons
rather than by individual pixels. Thus, outline fonts can be rescaled to any
size and displayed at any resolution with no degradation of appearance. (See
also: bitmapped font.)
outline highlight or location box
Shows which menu selection or button in a window is the object of keyboard
or mouse focus.
overlay
(vector or CAD) A transparent layer placed on an underlying image. The
overlay is where symbols, annotations, or image traces can be created or
displayed without changing the underlying image.
P
page layout
The process of selecting, sizing, and positioning multiple items to
compose a page for printing.
PA
Phase Alternating Line. A video standard generally used by the rest of
the world outside the United States and Canada that is not compatible with
NTSC.
pan
To move over an area of an image that is larger than the screen (visible
area), but is loaded to the display board.
panchromatic image
An image collected in the broad visual wavelength range but rendered in
black and white. The term has historically referred to a black and white
photograph of a color scene. Since the SPOT satellite 10-meter images are
collected over this broad visual spectral band and are usually rendered in
black and white, these images are called panchromatic.
pane
A resizable subarea of a window containing related options or components
and set off from other areas of the window by separators. The Tab key moves
the location box from pane to pane. The arrow keys move the location box
from component to component within one pane.
panel
A work area in a window composed of basic controls such as an array of
buttons and sliders.
parallelepiped classifier or decision rule
A simple form of automated computer interpretation slightly more complex
than boxcar interpretation. For parallelepiped classification, the
boundaries between classes need not be rectangular or parallel to the axes.
A parallelepiped area representing the location of each material sought is
prism-shaped in the 2-, 3-, or n-dimensional distribution of the available
multivariable images. (See also: boxcar classifier)
parallel port or parallel interface
A physical connection between a computer and a peripheral device, such
as a printer. A parallel port uses a connection that has more than eight
wires. Eight of the wires simultaneously convey the eight bits in a byte of
data, while the remaining lines control status information such as
"send me more" and "stop sending." DOS currently allows
the use of three different standard parallel ports, which are named LPT1,
LPT2, and LPT3.
parallels
Circles on the earth's surface, or lines on a map that are perpendicular
to the axis of the earth, and mark latitude north or south of the Equator.
parent object
An independent prime object in a project file related to some other
prime object below it in the project file hierarchy. An object linked by
HyperIndex to some other objects is the parent of those objects (referred to
as its daughter objects). (See also: daughter object, HyperIndex, index
area, link, stack.)
Paris classification
An unsupervised classification or clustering process developed by Dr.
Jack Paris and documented in: Jack F. Paris and Helenann H. Kwong (1988)
Photogrammetric Engineering and Remote Sensing 54(8):1187-1193.
Characterization of Vegetation with Combined Thematic Mapper (TM) and
Shuttle Imaging Radar (SIR-B) Image Data.
PAT
Point attribute table or polygon attribute table. A coverage can have either
a point attribute table or a polygon attribute table, but not both. In
addition to user defined allributes a PAT contains data on Area and
perimeter of a (Values are 0 for points) an internal sequence number and
feature identifier.
path
A DOS path is a description of the hierarchical chain of directories
that define the logical location of a file. For example, the path C:\FONTS\VFONTS.REF
is the complete path that describes the logical location of the VFONTS.REF
file which is in the \FONTS directory on hard disk C. The backslash
character (\) separates elements in a path. A Unix path is similar to a DOS
path, but the concept of drives are not given letter designations; they are
named like any directory. Hence, there are no colons in a Unix path.
pcARC/INFO
A vector-based Geographic Information System (GIS) developed and
marketed by ESRI, Inc. Unlike the parent minicomputer-based ARC/INFO, pcARC/INFO
presents a command-driven interface.
PCIPS
A raster-based microcomputer image processing system developed and
distributed by IBM. This is a menu-oriented entry-level system that runs on
standard color display cards such as CGA and EGA. PCIPS provides an
inexpensive and easy-to-use introduction to image processing.
PC-8
An 8-bit (256-character) IBM super set of the 7-bit ASCII character
encoding scheme that includes various symbols plus Latin characters with
diacritics. Printers and other output devices do not deal with the upper 128
characters in a standard fashion. Thus, what looks like an "i"
with two dots instead of one (ï, PC-8 character 139) on the screen may
print as something completely different. PC-8 makes different assignments
for codes 128-255 than does Latin-1, and thus is not a proper subset of
Unicode or ISO 10646.
pecabyte, Pbyte, or PB
A unit of computer measurement for (approximately) 1,000,000,000,000,000
bytes, 1,000,000,000,000 kilobytes, 1,000,000,000 megabytes, 1,000,000
gigabytes, or 1000 terabytes. (See also: bit, byte, exabyte, gigabyte,
kilobyte, megabyte, terabyte.)
pen
One type of pointing device (sometimes called a "stylus") used
with an X-Y digitizing tablet. It has a pencil-like feel which makes it
ideal for free-hand drawing. (See also: pointing device, puck)
pen plotter
An output device for line drawings that mechanically moves an ink pen
over the drawing surface.
photogrammetry
Obtaining precise measurements from images.
photointerpretation
Analyzing, measuring, and categorizing chosen features from airphotos.
physiographic
Describing the characteristics of a site's physical geography.
pictograph
A pictorial sign or symbol, for instance, representing a person with a
stick figure.
picture element or pixel
"The smallest element of an image that can be individually
processed in a video display system" (Random House).
Pinyin
(literally, "spell sounds") The phonetic alphabet based on
Latin letters adopted in the People's Republic of China in 1958 based on the
Beijing/Mandarin version of spoken Chinese.
pixel or picture element
"The smallest element of an image that can be individually
processed in a video display system" (Random House). The text and
images on a computer display are created by combinations of individual dots
(pixels). Different display hardware allows for more or fewer pixels on the
screen, determining the display resolution that is possible. The more rows
and columns of pixels, the finer the image detail that can be resolved.
pixel depth or color depth
The number of data bits each pixel represents. In 8-bit contexts, the
pixel depth is 8, and each display pixel can be one of 256 possible colors
or shades of gray. With a 24-bit raster (or with three coregistered 8-bit
rasters) the pixel depth is 24, and 16,777,216 colors are possible.
planimeter
"An instrument for measuring mechanically the area of plane
figures" (Random House).
planimetric map
A map designed to portray the horizontal positions of features; vertical
information is specifically ignored.
point element
A single point defined by a set of coordinates in space, and one of the
types of elements in a vector object. Point attributes include:
Point - in - Polygon
A topological overlay procedure which determines the spatial coincidence of
point and polygons. Points are assigned the attributes of the polygons
within which they fall.
Precision
It refers to the number of significant digits used to store numbers and in
particular, coordinate value. Precision is important for feature
representation, analysis and mapping. ARC/INFO supports single precision and
double precision.
Pseudo node
A node where two and only two arcsintersect or a single arc that connects
with itself.
Q
quad, quadrangle, map quad or map quadrangle
The geographic area covered by a map. One kind of map quadrangle is the
7.5' x 7.5' area that is covered by a standard USGS 7.5' topographic map.
Referring to a 7.5' map quadrangle does not imply the presence of an actual
paper map. The term may simply designate the area covered by electronically
stored materials.
Quad tree
A spatial index which recursively decompose a data set (eg image) into square
cells of different sizes until each cell has a homogeneous value. Quadtrees
are often used for storing raster data.
quantization
Dividing a continuous range into a finite set of discrete values called
quantization levels. If too few quantization levels are used, false contours
may appear in an image. Quantization levels are often referred to as
"gray levels," but the concept can also apply to color images.
query
A query, or database query, is a set of instructions defining attribute
criteria that are used to select records from a database. The Specific spatial
elements (such as lines or polygons) to which those records are attached are
then automatically selected for the current process.
R
radiance
"Radiant brightness or light: the radiance of the tropical sun"
(Random House).
radio button
A type of toggle button in a group of toggle buttons where only one of the
toggle buttons can be on at a time. A radio button is preceded by a graphic
indicator of the state of the button.
RAM
Random Access Memory. Read/write memory for programs and data that the
computer uses as a general work area. The more RAM in a computer, the more
general work space it has and the larger the projects it can handle. High
speed RAM can be added to a computer with memory expansion boards. The RAM
work area is accessed by numbered addresses that point to chunks of 1024 bytes
(a kilobyte or K). Standard DOS-based PC architecture limits the RAM a
computer can directly "see" to 640 K. Display boards generally have
their own memory and do not use system RAM.
RAM disk
RAM beyond the standard 640 K that is reconfigured to work like a very
high speed disk drive. DOS provides the VDISK command for setting up a RAM
disk (VDISK is documented in the DOS reference manual). Some microcomputers do
not allow a RAM disk in the memory in the address range between 640 K and 1024
K since it is used for DOS functions.
DOS uses a RAM disk just as it does any other disk drive. But since a RAM disk
is not a true magnetic storage device, its contents are lost when the
microcomputer is rebooted. Any permanent files must be copied from a RAM disk
to a magnetic disk before turning off or rebooting the computer.
range extraction
A method of converting a grayscale raster object into a binary version. In
range extraction, two boundary values are selected to bracket the desired
range of grayscale values. Everything above and below the boundary values is
set to 0 (black), while everything between the boundary values is set to 1
(white).
raster or raster object
A single, related, two dimensionally grouped set of numbers of a single
data type. Each number represents the value of some parameter. Its position in
the group represents its relative position to the other values. A raster
object is a raster that is stored in an RVC project file.
raster algebra
Manipulations and functions that operate on raster objects cell by cell.
Any raster object can be used as a variable, or operand, in a raster algebraic
expression. You just set up a combination of operands in an equation and then
assign a raster object to each operand. The result of the operation is stored
in a new raster object.
raster cell
One value in a raster that corresponds to a specific area on the ground. A
raster cell value may be the elevation above sea level at one position in a
survey site or the intensity of red radiation for a pixel in a video image.
For convenience, a raster cell is usually thought of as square or rectangular,
although many image collection devices actually measure circular or elliptical
areas.
raster space
The area of a raster object stored in an RVC project file. This area can
be very large, up to 2,000,000,000 by 2,000,000,000 cells.
RAT
Route attribute table. A RAT stores route attributes. There is one RAT for
each route-system in a coverage.
RDBMS
Relational Database Management System. A database management system with the
ability to access data organized in tabular files that can be related to each
other by a common field (items). An RDBMS has the capability to recombine the
data items from different files, providing powerful tools for data usage.
record
A database organized into tables, which contain records. Each record
supplies information gathered for an individual example. Records contain one
or more fields related to the topic of the table in which they are found. For
instance, the Crow Butte soil polygon database has a table of crop potentials,
and there is a record for each soil type. (See also: database, field, table.)
rectification
Removing geometric distortion from a raster or a vector object.
Rectification is usually achieved by aligning raster features or vector
coordinate positions with features in a base map or other coordinate reference
framework. Rectification may be used to bring several distorted image segments
into a common framework so they can be combined into a larger image.
reference image
An image on the display monitor used for visual reference that is
generated by (or otherwise corresponds to) a raster object or set of raster
objects. That is, you can use one raster object for the display, and another
raster object or set of raster objects for processing. In the simplest case,
you use the same raster object for both the processing raster object and your
reference on the display. In a more complex case, you use one raster object
for the display image, and a whole set of raster objects for processing. (The
processing set may include the display raster.) For instance, you could use a
raster object with a composite natural-color image of the study site for the
display, while using the seven raster objects containing the spectral bands of
the Landsat Thematic Mapper data for processing. (See also: processing rasters.)
region of interest
(Feature Mapping) Defines the area of the input raster objects to be
considered for all subsequent processing while that region is selected. A
selected region of interest affects the categories that can be defined, limits
the area in which cells that satisfy the decision rule are searched for, and
defines the region of the feature mapped raster for which measurements are
tabulated in Feature Mapping's statistical report. Feature marking is also
limited to the region of interest. (See also: categories, feature mapping.)
registration
Geometrically aligning sets of image data such that corresponding features
are coincident. (See also: coregistration.)
regression line
A line that best describes all the data points using a particular method
of error estimation, such as least squares.
relief
(as in shaded relief) The variation in a raster object's values that shows
differences between a surface's higher and lower parts in elevation and slope.
Remote Sensing
Acquiring information about an object without contracting it physically.
Methods include aerial photography, radar and Satellite Imaging.
render
Create an electronic or hardcopy representation, particularly of an
outline font. When an outline font is rendered, it assumes a fixed size and
shear angle on the screen, raster, or hardcopy to which it is rendered.
resample
To interpolate cell values in a raster object and create a raster with
larger or smaller cells. (See also: interpolation.)
resize
To change the height and/or width of a window.
resolution
The level of object detail or sharpness determined by how many picture
elements compose an area of a display or corresponding raster. Resolution may
refer to sensors, raster objects, or displays. Low resolution display devices
produce images with a grainy visual texture. High resolution displays use such
small picture elements that they can produce a near-photographic quality
image. (See also: ground resolution.)
resolution
(digitizer) The smallest movement that can be detected by the digitizer.
Resolution is usually expressed in either measurement units (.001") or
dots-per-inch (1000 dpi).
restitution
The determination of the true (map) position of objects or points; the
image of which appears distorted or displaced on unprocessed aerial
photographs. Restitution corrects for displacement resulting from both tilt
and relief displacement. Restitution in classic photogrammetry is commonly
achieved by analytical methods or through the use of stereoscopic plotting
instruments.
RGB
Red, Green, and Blue. The red-green-blue color model uses position within
a cube to describe colors. The axes of the cube are the red, green, and blue
values. The shades of gray are found along the diagonal from the origin of the
cube, where red, green, and blue values are zero and the apparent color is
black, to the opposite corner, which appears white (red, green, and blue
values are 100%). RGB is generally used in reference to the separated spectral
bands of an image so that the red, green, and blue bands taken together create
a natural color image. (See also: HBS, HIS.)
RGBB
A display method that converts an RGB raster set into an HBS raster set
and then substitutes a fourth coextensive raster object for the brightness
component before conversion back to RGB components for display. The object
selected for the brightness component is generally of higher resolution than
the objects selected for the RGB components and imparts a higher
pseudo-resolution to the displayed image. (See also: HBS, RGB.)
RGBI
A display method that converts an RGB raster set into an HIS raster set
and then substitutes a fourth coextensive raster object for the intensity
component before conversion back to RGB components for display. The object
selected for the intensity component is generally of higher resolution than
the objects selected for the RGB components and imparts a higher
pseudo-resolution to the displayed image. (See also: HIS, RGB.)
RGB set
A set of coregistered, coextensive rasters that represent the red, green,
and blue bands of an image.
RGB video
A video image composed of separate red, green, and blue signals. RGB video
is a general term that applies to different technologies (analog or digital)
and standards (like TTL and RS-170).
root window
The main window of the X server. Each client process runs as a subwindow
within the root window. On DOS/Windows 3.1 systems, you can choose to display
the MicroImages X Server title bar if desired. Besides identifying the
MicroImages X Server, this title bar provides the pixel depth of the current
display mode, the screen resolution, and MicroImages' technical support
number.
row
A horizontal list of data values or display cells in a raster object or
display.
RS-170 video
A standard for RGB analog video in the USA that governs the form of the
RGB color signals. RS-170 video has a 15.7 kHz horizontal scan rate and a
30-cycle per-second frame rate. It is not modulated with a carrier as is
broadcast video.
rubbersheeting
Any process in which a raster is stretched differentially to match a new
set of geometric constraints. This shape change could be defined by any one of
many transformations such as changing a map projection, trilateration to
change the absolute position of cells within a raster, fitting a polynomial to
a surface, least squares movement of control cells, and so on.
RVC file
Raster/Vector/CAD formatted file. These files incorporate the benefits of
a 32-bit compiler. (See also: project file.)
RVF file
Raster/Vector Format(ted) file. The DOS extension for all MIPS project
files is .RVF. When looking for project files, MIPS searches and accesses only
files with a .RVF extension. (See also: project file.)
S
SAIF
Spatial Archive and Interchange Format. SAIF is the Canadian draft National
Standard for Geomantic Data Interchange. Designed originally by the Government
of British Columbia, it is a specification for data, which includes an object
oriented data model and a language for describing both spatial and non spatial
data.
samples
Groups of cells in an image selected to represent one feature type or land
cover of interest. You define samples from your knowledge of the site. (See
also: prototypes, training sets.)
sample set
For unsupervised classification processes, a set of sample cells that is
selected from the input raster set and used to automatically define classes.
The selection of the sample set during processing is controlled by a sampling
interval (in line and column directions).
sampling
The process of approximating an image using a subselection of pixels.
Sampling is usually done at constant intervals though this is not required.
Generally, as the number of samples increases, the quality of the image
increases. (See also: resample.)
SAN
System network architecture. Networking protocol popular in IBM environments.
SAR
Synthetic Aperture Radar.
sash
A small graphic control component on the separator between two panes. A
sash moves the separator to change the size of the panes. Drag the sash with
the mouse to make a pane larger or smaller.
Satellite Image
A picture of the earth taken from an earth orbital satellite. Satellite images
may be produced photographically or by on-board scanner (eg MSS)
saturation
One of the three coordinates that the HBS and HIS color domains use to
define a display color. Saturation designates how far away a color is from a
gray or neutral color of equal intensity. (See also: HBS, HIS.)
scalar
An SML variable for numeric values. The SML naming conventions presume any
variable that begins with a lower case letter is a scalar value or a string.
scale value
A number used as a multiplier to translate a set of numbers from one range
of values into another. For example, a set of decimal values that range
between 0 and 2 could be projected into the numeric range of 0 to 100 by
multiplying each number in the set by a scale value of 50.
scanner
A digitizer that produces an image (raster object) from flat input
material such as photographs, maps, and drawings.
SCIAMACHY
SCIAMACHY is a spectrometer that maps the air over a very wide wavelength
range, which allows detection of trace gases, ozone and related gases, clouds
and dust particles throughout the atmosphere. It works by measuring sunlight,
transmitted, reflected and scattered by the earth's atmosphere or surface in
the ultraviolet, visible and near infrared wavelength region. With a 960-km
swath it covers the entire world every six days. John Burrows of the
University of Bremen's Institute of Environmental Physics first devised the
idea for SCIAMACHY, and he now serves as its Principal Investigator. SCIAMACHY
is part of a family of atmospheric spectrometers that also includes GOME on
ERS-2 and the forthcoming GOME-2 instrument launching next year with the first
MetOp mission
scroll
"To move the current text or image up, down, or across the monitor so
that new text or image appears on one edge of the screen as it disappears from
the other" (Random House). Scrolling is controlled with the mouse and the
arrow keys. For example, a list of objects in a project file which is too long
to fit on the text screen can be scrolled up and down with the vertical arrow
keys.
scroll bar
Indicates position of current view in relation to the whole, and used to
change the user's viewpoint. The scroll bar consists of a slider, scroll area
("trough"), and scroll arrows.
SCS
Soil Conservation Service. A service of the United States Department of
Agriculture.
SCSI port
Small Computer Systems Interface (SCSI is pronounced "skuzzy.")
A physical connection between a computer and a peripheral device, such as an
external hard drive or optical drive.
seam
The junction in the area of overlap between raster objects combined by
tiling or mosaicking.
SECAM
Sequential Couleur à Memoire. A video standard used in France and the
former USSR.
sections of land
The U.S. Public Land System divided much of the U.S. into square sections
of land with an area of approximately square mile (sides 1 mile long). Since
most of this survey was completed in the late 1800s, these sections vary
greatly in area and shape. In some areas survey adjustments have created
sections as big as
square miles. Sections are the basic unit of land ownership in the central and
western U.S. They are usually bounded by roads that give rise to the
checkerboard land patterns characteristic of these areas.
seed point
The seed point for a watershed is the lowest point in a watershed, or the
point to which all other points drain. The seed point for a flow path is the
highest point of the path. Water flows from there to a watershed seed point or
the boundary of the study area.
segment
A segment is a line or polygon that forms part or all of a glyph. A glyph
made from polygons will be filled when printed but may optionally be displayed
in outline form to increase display speed. A glyph made of line segments
rather than polygons is known as a stroke font. It is faster for the computer
to draw a stroke font than a font made of polygons. The ability to create
stroke fonts in the Outline Font Editor is not yet implemented.
select
To mark one or more of a group of elements in preparation for acting upon
them by some program operation such as move, copy, edit, open, analyze,
display, or delete.
select button
The mouse button used to make a selection.
selection box
(more properly called the location box) A graphical symbol that marks the
current location of keyboard focus for an operation. Moved with Tab and arrow
keys.
selection highlight
An item displayed in reverse video in a text list, that indicates which
member of the list is selected. You complete the selection by pressing the
<Enter> key (or double clicking with the left mouse button).
selection query
(in database queries) A selection query is constructed from one or more
comparison expressions. Only if the entire query evaluates to "true"
(non-zero) for an element, is the element included.
selection set
All elements currently selected by the Element Selection tool for viewing
or editing make up the selection set. One element in the selection set,
generally the last element selected, is the active element. Attribute
assignments and editing changes can be applied to just the active element or
to all elements in the selection set. (See also active element.)
separator
A dividing line that marks a logical division between areas of a window or
menu.
serial port
A physical connection between a computer and a peripheral device, such as
a plotter. A serial port uses a connection that has at least three wires. (The
standard IBM AT serial port uses nine wires.) The eight bits in a byte are
transmitted serially, or end to end, through a single line while the remaining
lines contain status information such as "send me more" and
"stop sending." DOS currently allows the use of two different
standard serial ports named COM1 and COM2.
shaded relief
See - relief
shear
Angular slant given to a vector font to produce the effect of italics.
shift sequence
A keyboard technique for text entry in a language that uses more than one
character set, such as Japanese which uses a mix of ideographs, Latin
characters, and Japanese phonetic characters. The user enters a shift sequence
to indicate a switch from one character encoding scheme to another.
Electronically, each character is preceded by a shift sequence byte that
identifies its character set.
SIF
Standard Interchage Format, a spatial data exchange format. A standard or
neutral format used to move graphics files between computer systems.
slider
A graphic control component that controls the setting of a variable. Move
the slider by dragging it with the mouse to make its associated value larger
or smaller.
Sliver
A gap formed when two lines which should be continuous are slightly separated
in a graphical representation or map.
Slivers polygon
A small area feature commonly occurring along the borders of polygons
following the topological overlay of two or more coverages.
slope
A measure of how steeply a surface or line inclines. Slope is computed by
dividing a line's vertical rise or fall by the distance the line travels on
the surface (the "rise over the run") - usually expressed as a
percent.
smart line following
An interactive process for converting raster line images to line elements
in a vector object. The user clicks on a line image, and the process follows
the line, over-tracing a vector line. The process stops at the edge of the
raster, at the end of the line, or at a spaghetti junction of lines that the
user must guide it across.
SML
Spatial Manipulation Language. A programming language for manipulation of
raster, vector, and CAD objects provided by the Map and Image Processing
System. SML allows you to enter either immediate commands or to write a full
program. To use SML interactively, you enter single commands from the keyboard
and SML executes each command as it is entered. To use structured programs
with SML, you prepare a program file ahead of time.
soil association
A soil mapping unit containing adjacent soils, but the survey did not take
the time and effort to delineate them. Soil association information is
suitable for general planning only: to compare areas, to locate refuge tracts,
and certain kinds of land use.
soil complex
A soil mapping unit with two or more soils so intricately mixed that they
cannot be shown separately on the map.
soil group
(undifferentiated) A soil mapping unit with two or more soils. For the
purposes of the map, there was little value in separating them.
soil mapping unit
An area on a soil map with a complete, closed border drawn by a soil
scientist, usually representing an area of one type of soil. A mapping unit is
nearly equivalent to a soil phase with the exception of small scattered bits
of other soils that are not worth showing.
soil phase
A subset of a soil series differentiated by slope, stoniness, or other
characteristics that affect the soil's usefulness.
soil profile
The sequence of natural layers, or horizons, in a soil. A profile extends
from the surface down into the parent material that has not been changed much
by leaching or by the action of plant roots.
soil series
A U.S. category of soil classification including soils that have similar
profiles (thickness, arrangement) named for a town or geographic feature near
its first observation. Soils in a series are essentially alike in
characteristics that affect their behavior in an undisturbed landscape.
solid modeling
The process of rendering a 3D surface from vector type data. This process
is widely used in CAD software packages to prepare a realistic color
presentation of a component part, a building, or other solid object from
complex vector-oriented engineering drawings. In GIS vector-oriented software,
contours of the surface of the land stored as vectors might be used to render
a solid model of the land's surface.
spaghetti digitizing
Entering line data in no particular order using a digitizer.
SPANS
The SPatial ANalysis System from TYDAC Technologies.
spatial
An adjective applied to objects that vary in space in two or three
dimensions.
Spatial Manipulation Language
See - SML
spectral band or spectral region
A well-defined, continuous wavelength range in the spectrum of reflected
or radiated electromagnetic energy. Red, green, and blue are all spectral
regions within the portion of the spectrum that is visible to humans as light.
Color-infrared images are composed of red, green, and a spectral region
commonly called the photoinfrared, which is not in the visible portion of the
electromagnetic spectrum. (See also: color-infrared, electromagnetic
spectrum.)
spheroid
Any shape that closely resembles or approximates a perfect sphere. In the
context of map projections, a spheroid is an ellipsoid of rotation that is
flattened at the poles, like the earth.
spline
An interpolating polynomial for a set of coordinate points used to fit a
curve that connects the points. (See also: Bézier curve)
SPOT
The French Systeme Probatoire d'Observation de la Terre. There are two
SPOT satellites: one collects images with 10-meter ground resolution in a
single panchromatic spectral region; the other collects 20-meter images in the
three spectral regions used for color-infrared maps. SPOT satellites may be
pointed at an angle off-axis or off-nadir to collect forward and rearward
images: a technique that yields stereoscopic image pairs from which accurate
elevation rasters can be computed.
spread
The spread operation changes the colors between two selected tiles in the
Color Map Editor window.
spur
A false line segment that extends a short distance beyond a T-junction of
two lines. Binary raster thinning processes often leave spurs that should be
erased by raster editing before final vectorization.
SQL
Structured Query Language. A Syntax for defining and manipulating data from a
relation database. Developed by IBM in 1970 s, it has become an industry
standard for query languages in most relational database management system.
SRG
Standardized raster graphic, a digital representation of a map or chart which
is captured by automatic digitization (scanning), stored on a digital storge
media and displayed on a raster screen or raster plotter, obtained by a
regular scan of a paper map or chart or repromat. It consists of a raster data
set of RGB intensities or colour (SIC) coded.
stack
A hierarchical arrangement of images and other information used by
HyperIndex that graphically links logically related objects or files. A stack
has the inverted tree form of a genealogy chart. (See also: HyperIndex, link.)
standard parallel
A parallel of latitude used as a control line in the computation of a map
projection, and which is therefore, true to scale. Some map projections have
no defined standard parallel, others have one, while others have two.
standard 64 annotation colors
In 8-bit contexts the Color Map Editor window normally reserves the first
64 colors for a standard set of user annotation colors for text and overlays.
That leaves 192 colors for the image itself - ample color space for
representing most natural color images to the human eye. The 64 standard
colors are chosen at fixed intervals in the RGB color model. They generally
appear brighter and purer than the subdued natural tones of the underlying
image.
State Plane Coordinate System or SPCS
The State Plane Coordinate System (SPCS) defines map coordinates by zone
for the United States. Each zone has one central meridian and scale factor,
which permits all USGS quadrangle maps in a zone to be mosaicked exactly.
Zones with north-south extent use the Transverse Mercator projection, while
those with east-west extent use Lambert Conformal Conic. (The panhandle of
Alaska is the only exception, and uses Oblique Mercator).
stepwise linear classification
A supervised image processing routine applied in the same fashion as
maximum likelihood classification using training sets, or prototypes. This
method applies the classical techniques of stepwise linear discriminant
analysis to set up the classification model and map the materials desired from
the input raster objects. (See also: maximum likelihood classification)
stereo elevation
An elevation surface derived from stereo pairs of remote sensing imagery.
For example the SPOT satellite can collect an "off nadir" image and
then in a subsequent fly-over collect its counterpart to make a stereo pair.
The stereo elevation process takes the 3D effect of that stereo pair to derive
an accurate raster object of elevation values.
style query
(in database queries) A style query is constructed from a combination of
comparison expressions, which examine values of element and database
variables, and assignment statements, which set the values of drawing
variables.
subtractive color
Creating color by using absorption or scattering to selectively remove
some of the colors of light, or radiation, reaching the human eye is a
subtractive process. The use of pigments, such as color printing or a
painting, demonstrate this subtractive color process. The greater the number
of different colored pigments mixed together, the darker a pigmented object
appears. This darkness results from an increased absorption of visible light
by the pigments and, consequently, less light reflected to the eye. The
presence of fewer pigments or their absence altogether results in greater
reflectance of visible light. Selective absorption removes a color(s) from the
reflected radiation and results in the perception of the complementary color.
subwindow
An auxiliary window that opens as the result of some user action in the
parent window (such as pressing a button), or of some processing condition (a
dialog box subwindow might open with a message or warning.)
Suits-Wagner classification
A simple form of supervised or semiautomatic classification that operates
similarly to a boxcar or parallelepiped classification. This method defines
the sides of the box for each class as plus and minus one standard deviation
from the mean of the values of the prototype, or sample, values selected to
represent that class. This method has the advantage that like a simple boxcar
classifier, it is very fast to apply the resulting decision rule to the
unknown pixel values. More information on this process can be found in: H.L.
Wagner and G.H. Suits (1980) Proceedings of the 14th International Symposium
on Remote Sensing of the Environment, vol. III pp. 1525-1529. Environmental
Research Institute of Michigan, Ann Arbor Michigan. A Low Cost Classification
Algorithm for Developing Countries.
supervised classification
A type of automatic multi-spectral image interpretation in which the user
supervises feature classification by setting up prototypes (collections of
sample points) for each feature, class, or land cover to be mapped.
surface fitting
Techniques that use 3-dimensional vector point data to create a raster
object containing an elevation surface. Various methods can be used to fill
the gaps between the vector points and derive the elevation values for the
intermediate raster cells.
SVHS video
Super VHS video. A newer video standard for cameras and recorders. SVHS
equipment achieves a higher resolution than conventional VHS equipment. SVHS
overcomes some of the VHS band width limitations by maintaining the video in
two separate components and signals.
symbol overlay
A vector object can have symbol shapes assigned to some or all of its
point features. When this vector object is displayed over (or overlaid on) an
image, you can also choose to display the symbols over the top of the features
in the underlying image. Such symbols may also be attached to database records
and used to graphically retrieve such reference information. For example, a
symbol overlay that uses ducks to represent nesting sites could be shown over
a habitat map. A click on a particular duck symbol could retrieve a record
from an associated database and display it on the text screen to provide such
information as the date of first occupancy, number of eggs, number of
fledglings, and so on. (See also: overlay.)
symmetric minima
A raster cell that has a value less than two opposite neighbors in any
direction. A raster object of symmetric minima is calculated from an elevation
raster object and provides a representation of the relative roughness of
terrain.
synthetic resolution
An apparent increase in spatial resolution achieved either by resampling
image rasters or by combining images from different sensors of varying
resolutions (such as SPOT panchromatic and TM multispectral).
nts or their absence altogether results in greater reflectance of visible
light. Selective absorption removes a color(s) from the reflected radiation
and results in the perception of the complementary color.
subwindow
An auxiliary window that opens as the result of some user action in the
parent window (such as pressing a button), or of some processing condition (a
dialog box subwindow might open with a message or warning.)
Suits-Wagner classification
A simple form of supervised or semiautomatic classification that operates
similarly to a boxcar or parallelepiped classification. This method defines
the sides of the box for each class as plus and minus one standard deviation
from the mean of the values of the prototype, or sample, values selected to
represent that class. This method has the advantage that like a simple boxcar
classifier, it is very fast to apply the resulting decision rule to the
unknown pixel values. More information on this process can be found in: H.L.
Wagner and G.H. Suits (1980) Proceedings of the 14th International Symposium
on Remote Sensing of the Environment, vol. III pp. 1525-1529. Environmental
Research Institute of Michigan, Ann Arbor Michigan. A Low Cost Classification
Algorithm for Developing Countries.
supervised classification
A type of automatic multi-spectral image interpretation in which the user
supervises feature classification by setting up prototypes (collections of
sample points) for each feature, class, or land cover to be mapped.
surface fitting
Techniques that use 3-dimensional vector point data to create a raster
object containing an elevation surface. Various methods can be used to fill
the gaps between the vector points and derive the elevation values for the
intermediate raster cells.
SVHS video
Super VHS video. A newer video standard for cameras and recorders. SVHS
equipment achieves a higher resolution than conventional VHS equipment. SVHS
overcomes some of the VHS band width limitations by maintaining the video in
two separate components and signals.
symbol overlay
A vector object can have symbol shapes assigned to some or all of its
point features. When this vector object is displayed over (or overlaid on) an
image, you can also choose to display the symbols over the top of the features
in the underlying image. Such symbols may also be attached to database records
and used to graphically retrieve such reference information. For example, a
symbol overlay that uses ducks to represent nesting sites could be shown over
a habitat map. A click on a particular duck symbol could retrieve a record
from an associated database and display it on the text screen to provide such
information as the date of first occupancy, number of eggs, number of
fledglings, and so on. (See also: overlay.)
symmetric minima
A raster cell that has a value less than two opposite neighbors in any
direction. A raster object of symmetric minima is calculated from an elevation
raster object and provides a representation of the relative roughness of
terrain.
synthetic resolution
An apparent increase in spatial resolution achieved either by resampling
image rasters or by combining images from different sensors of varying
resolutions (such as SPOT panchromatic and TM multispectral).
T
tab group
(also, "Field") A component of a window such as a button, list,
scroll bar, pane, sash, or slider (sometimes "scale") that can be
selected with the location box by pressing the Tab key. Some tab groups, such
as a selection list, can be composed of multiple items through which the
location cursor can be moved by the arrow keys.
table
A database is organized into tables that contain records. Tables cover
different topics related to the same common theme. The theme and its extent of
development determine the number of tables that comprise the database. For
example, the Crow Butte soil polygon database contains twelve tables, in such
areas as yield, crop potential, and statistical information. (See also:
database object, field, record.)
TARGA file
Truevision Advanced Raster Graphics Adapter file. A file saved or loaded
from an ICB, TARGA, or VISTA display board in one of several related TARGA
formats. These formats are widely used with other boards and software to
transport color images between microcomputer software and systems.
TAT
Text AttributeTable for an annotation subclass in a coverage. In addition to
user defined attributes, the TAT contains a sequence number and text feature
identifier.
terabyte, Tbyte, or TB
A unit of measurement for (approximately) 1,000,000,000,000 bytes,
1,000,000,000 kilobytes, 1,000,000 megabytes, or 1000 gigabytes. (See also:
bit, byte, exabyte, gigabyte, kilobyte, megabyte, pecabyte)
Terra-Mar
A vendor of a second-generation raster-based microcomputer image
processing and GIS system.
text
A string of characters grouped in a file.
text cursor
A graphic mark such as a blinking underscore, vertical line or
character-sized box on the screen that indicates the focus of keyboard text
entry and editing.
text field
A component of a window that can be selected with the location box for
textual information that can be entered and edited from the keyboard.
text monitor or text screen
The B/W or color monitor used to display text materials (like menus,
database records, and keyboard input).
text object
Anything from a simple string of ASCII characters to a more complex,
formatted page description.
thinning
(rasters) To remove cells from wide line images in a raster object. When a
scanner creates a raster object, the lines in the drawing typically are
several cells wide in the result. Before automatic vectorization techniques
can work on the data, the line images in the raster object must be thinned to
make the line images just one cell wide.
thinning
(vectors) Reducing the number of coordinate pairs that describe a vector's
line and polygon elements. Some of the coordinate pairs will be discarded when
straight line lengths replace curved or noisy segments in the original lines.
threshold
(binary) The separation point for converting grayscale raster cell data
into binary (black and white) data. For a raster object scanned with 256
levels of gray, a threshold might be set at 180. Then the output binary raster
object would have a 1 for every cell in the input raster object that had the
value 180 or higher, and 0 everywhere else.
thresholding
Setting a data conversion separation limit such that any incoming value
above the designated limit, or threshold, is assigned one value (in binary
thresholding, a "1") and any incoming value below or equal to the
limit is assigned another value (in binary thresholding, a "0").
Thresholding is often used to generate a binary raster from a 16-gray-level
scan, or to find feature edges during the steps of raster to vector
conversion.
tie point
A point that is co-located on two raster objects that have an overlapping
geographic extent. Tie points are used in the manual mosaic process to
establish the relationship between adjacent pieces of the mosaic that provide
no absolute ground control information, but do show some common ground feature
in each piece. For example, multiple frames of airvideo can be tied together
with tie points (farm buildings, field corners, bushes, rock outcroppings,
bends in streams) even if the map coordinates are not known for such features.
Then, the map calibration for the entire sequence can be established from
control points sparsely located in the mosaic sequence (such as road
intersections) for which the map coordinates are known. (See also: control
point .)
TIFF
Tag Image File Format. A series of standard color image file formats
adopted by Microsoft, Aldus, and others to transfer images between different
software packages.
TIGA
Texas Instruments Graphics Architecture. A software interface that
standardizes communication between application software and display boards
that use one of the TMS340 chips and can be used to interface with several
manufacturers' image display boards. TIGA divides tasks between the TMS340
display processor and the CPU of the host microcomputer to improve
performance.
TIGER files
Topologically Integrated Geographic Encoding and Referencing files
compiled and distributed by the U.S. Census Bureau.
tiles
Rectangular areas of defined size in a raster object used for storage of
the information. Storing raster objects in tiled format generally increases
display speed when viewing less than the entire object.
A third usage of the word tiles occurs in the Color Map Editor where the upper
part of the window displays the colors in the map with small sample squares or
tiles. The active or selected tile is outlined in white, and its cell value
and a larger sample is displayed below.
tiling
Assembling large images from smaller segments that have common angular
orientations, cell sizes, and map projections. The process is similar to that
of assembling floor tiles, except that the raster tiles may overlap at the
onset. (See also: montage, mosaic.)
tin
Triangulated Irregularr network. A surface representation derived from
irregularly spaces, sample point and breakline features. The tin dataset
includes topological relationship between points and their neighbouring
triangles. Each sample point has an x, y coordinate and a surface or z value.
These points are connected by edges to form a set of non overlapping triangles
used to represent the surface. Tins are also called irregular triangular mesh
or irregular triangular surface model.
TIN Densification
A DEM extraction method that builds a TIN surface from the initial set of
user-supplied tie points, and then iteratively densifies the TIN object. The
process looks in the middle of each existing triangle and adds a new node when
it finds a point of high correlation. Then it recomputes the local topology
and goes on to the next triangle.
TIN elements
TIN objects contain four element types: nodes, edges, triangles, and
hulls. Nodes are the most fundamental element of a TIN and the only element
type that references spatial coordinates (x,y,z). An edge is an oriented line
segment that connects two nodes. Three edges connect three nodes to form a
triangle that satisfies the Delaunay criterion. Triangles represent elementary
areas of the surface that describe topological relationships between all other
elements of the TIN data. A hull represents the area covered by a TIN
structure. Interpolation of z-values is only valid within a hull region.
TIN object
A TIN, or Triangulated Irregular Network, object represents a continuous
surface as a set of conterminous triangles computed from irregularly spaced 3D
points. TIN topology is more restrictive than the topology of other coordinate
data objects; every node is part of some polygon, every polygon is a triangle,
and every triangle satisfies the Delaunay criterion. (See also: Delaunay
criterion.)
title bar
The area across the top of a window that displays the name of the window,
the resize graphic, and the iconifying button.
TM
Thematic Mapper. A sensing device on the Landsat satellite that scans and
stores 7 individual images in spectral bands ranging from the blue wavelengths
up to those in the thermal infrared.
toggle button
A toggle button offers an on/off control option for the current process. A
toggle button's label tells what state it controls, and it is preceded by a
graphic indicator of the on/off state of the button.
toolTip
A ToolTip pops in naming the menu item selection that diplicates the
function of the icon button when the mouse cursor pauses over an icon button.
topographic map or topo map
A map that uses colors and symbolic patterns to represent the general
surface features of the earth, such as grassland, forest, marsh, agricultural,
urban, and barren rock.
topography
The features of the actual surface of the earth, considered collectively
according to their form (for example, grassland, cultivated, desert, forest,
swamp). A single feature, such as one mountain or one valley, is called a
topographic feature.
topology or vector topology
A description of the relationship between node, line, and polygon elements
in a vector object. An RVC vector object has a rigorously defined topology,
which keeps track of things like lines that intersect at nodes, polygon
elements on either side of a line element, line elements that form a polygon,
island polygons within polygons, and parent polygons for island polygons.
topology errors
Violations of vector topology, such as line elements that intersect
without a node at the point of intersection, or polygons that overlap without
defining an intersection polygon.
trace
To create a vector line element by manually or interactively tracing over
line images in a raster object.
training set or prototype
A group of sample cells in an image known to represent a feature type or
ground cover of interest defined by the user from his or her knowledge of the
site (perhaps through ground visitation or detailed airphoto interpretation).
transcoder
A device that converts video signal formats from an input type (like SVHS)
to an output type (like RGB analog).
transfer rate
The number of XY coordinate pairs produced per second when you are
digitizing with the streaming method.
Transformed Vegetation Index
A commonly used vegetation index derived from images of certain spectral
bands. The TVI is equal to the square root of the quotient of the
photo-infrared minus the red band, and the photo-infrared plus the red band {SQRT[(IR
- red) / (IR + red)]}.
translation curve
The curve used to adjust a raster object's cell values to the brightness
values used for display.
transliterate
To represent the words of one language, with the alphabet of another
language. Usually the language is foreign to the reader, and the alphabet is
familiar.
transparent color
The ability to overlay one color image over another image or map so that
the spatial details of both are revealed for comparison is achieved with
transparent color. The colors that result from such an overlay depend on
whether the color in the images is additive or subtractive.
transparent patterns
Patterns that only partially obscure the image upon which they are
superimposed are transparent. For example, a pattern could consist of a
drawing of a duck that leaves the remainder of the pattern tile transparent.
When this pattern is used to fill a polygon that contains a lake, the lake
colors and features will be visible through the transparent portions of each
tile.
true scale
At large sizes, every map projection distorts the scale of distance,
especially towards the edges. The location of the true scale of a projection
identifies the position where map measurements correctly correspond to actual
surface distances.
TSR
Terminate and Stay Resident. A software process that becomes resident in
memory when executed and monitors your input or the actions of other programs
and performs some special activity when the appropriate conditions are
detected. For example, A TSR program may be loaded to memory and wait for you
to enter a particular non-standard series of keystrokes to initiate printing
your text screen out on paper.
TVI
See - Transformed Vegetation Index
TYDAC
A raster-based commercial GIS system.
U
underlay
To place a raster object so that it appears to be behind an existing
object or image and will show around the perimeter and through any internal
data holes in the object on top.
undershoot
An arc that does not extend far enough to intersect another arc.
Unicode
A character encoding scheme that is a super set of ASCII and Latin-1 with
room for 65,536 characters (a 16-bit or 2-byte set). (Over 28,000 characters
have been assigned so far.) The Unicode standard is still in committee; it is
in the care of the International Organization for Standardization (ISO) and
Unicode, Inc. (formerly the Unicode Consortium). Unicode itself is a subset of
ISO 10646, and in terms of ISO 10646, Unicode is the "Basic Multilingual
Plane." Unicode will include all characters needed for the written
languages of the modern world.
unsupervised classification or automatic interpretation
The operation of a group of multispectral image interpretation functions
(such as K-means) that statistically cluster cells into similar collections.
When the classification procedures are complete, you identify and label the
ground features or conditions that the clusters represent.
USDA
United States Department of Agriculture.
USDI
United States Department of the Interior.
USF&WS
United States Fish and Wildlife Service of the USDI.
USGS
United States Geological Survey.
UTM
Universal Transverse Mercator map projection.
V
variable
(in database queries) A named entity that has an assigned value. There are
four kinds of query variables: (1) those are associated with the vector
elements (like numlines, class, and startnode); (2) those which are fields
from a database (perhaps Name, Acres, and Yield); (3) those which control the
drawing styles of vector elements (like size, color, and fillcolor); and (4)
the ten temporary user variables for numeric operations (temp0, temp1, temp2
... temp9). For example, the point element variable "size" can have
a value from 1 to 64. It controls the size at which a point element is drawn.
An assignment statement can change only the values of drawing style and
temporary variables; it cannot change the value of variables that are
associated with a vector element or a database.
VAT
Value Attribute Table. A table containing attribute for a grid. In addition to
user defined attributes, the VAT contains the values assigned to cell in the
grid and a count of the cells with those values.
vector
"A quantity possessing magnitude and direction, represented by an
arrow, the direction of which indicates the direction of the quantity and the
length of which is proportional to the magnitude" (Random House). In
connection with GIS and computer graphics, this term is used more loosely to
refer to a set of vectors joined end to end to make an arc or irregular line
with a uniform set of properties.
vector element
A vector object is made up of three different types of elements that can
have associated attributes 1) points, which are single sets of coordinates
that define a point feature (such as a well); 2) lines, which are curvilinear
strings of coordinates that define a curved line (such as a stream); and 3)
polygons, which are collections of lines that inscribe an area (such as a
lake), and a fourth type of element, nodes, which are necessary to maintain
vector topology.
vector format
A data structure for representing point and line data by means of 2- or
3-dimensional geometric (Cartesian x,y or x,y,z) coordinates with exacting
topological requirements. In connection with GIS and computer graphics,
"vector" can refer to a set of line segments joined end-to-end to
make a curved path in space. Vector objects also have a set of attributes
(such as ID number, color, drawing style) attached to them.
vectorize
A general term for any technique that converts raster data into vector
data.
vector object
A collection of vector elements and attributes stored in a complex
topology as one entity project file. (See also: vector topology)
vector topology
A description of the relationship between point, node, line, and polygon
elements in a vector object. An RVC vector object has a rigorously defined
topology, which requires that points can be in at most one polygon and lines
do not intersect without separation by nodes, which are required for topology
maintenance.
vegetation index
The output from standard manipulations of multispectral image raster
objects. The system processes the input spectral information and creates
output raster objects whose cell values represent the site's biophysical
properties: amount of vegetation, leaf area, greenness, brightness, and
wetness.
VersaCAD
A popular, commercial microcomputer Computer Aided Design (CAD) software
package developed and marketed by PRIME.
vertex
The point at which a line changes direction or terminates.
VESA
Video Electronics Standards Association. A microcomputer graphics standard
with support for 256 simultaneous colors.
VGA
Video Graphics Array. A microcomputer video subsystem introduced by IBM
with the PS/2 microcomputer in 1987 with support for 256 simultaneous colors.
The VGA is an enhancement of the older EGA and is now also available for other
AT bus based microcomputers. (See also: CGA, EGA.)
VHS
Video Home System. A popular format for low-cost video recording and
playback, common in home video systems.
video capture
Some image display boards have the ability to display live broadcast or
taped programming and then freeze and grab an image, storing it in the
computer's memory or on disk.
video digitizing board
A video interface circuit board installed in a PC that samples or
frame-grabs a video frame and constructs a digital image. Video digitizing
boards can be used for non-standard, higher resolution video sources. (See
also: frame-grabbing.)
video field
The image you see on a standard TV screen is composed of a set of about
480 horizontal lines. The lines are projected in two passes of the signal
beam. Each pass only projects every other line of the image: the odd lines in
one pass, and the even lines in the next pass. One scan takes 1/60 of a
second, so the whole picture (the frame) is refreshed every 1/30th of a
second.
A field contains every other line of the complete video image. The primary
field contains the odd lines; the secondary field contains the even lines.
video frame
A complete video image, which consists of two interlaced fields Odd lines
of the frame are contained in the primary field which is alternated with the
secondary field which contains the even lines. The primary field lasts 1/60 of
a second in standard broadcast video. The secondary field follows in the next
1/60 of a second. The entire frame takes 1/30 of a second to display. There is
a difference of 1/60 of a second between alternate lines in the image.
viewshed
The boundaries of sight from a single vantage point, assuming an
unobstructed surface (disregard trees and buildings
vignetting
Darkening at the edges and corners of an optical image. Vignetting occurs
because lenses are physically unable to pass as much light to the fringe of an
optical field as they d
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