E
easting
A rectangular (x,y) coordinate measurement of distance east from a north-south reference line, usually a meridian used as the axis of origin within a map zone or projection. False easting is an adjustment constant added to coordinate values to eliminate negative numbers.
edge conditions
In agricultural row crop imagery, the biomass values for cells in the middle of a healthy row are high, while the thin plant fringes or bare soil between rows have low biomass values. Low biomass values along the edges of healthy rows are normal and are no cause for concern. But edges cannot be distinguished by value alone from the low biomass values of regions of insect or disease damage which must be identified and given special attention.
edge mapping
An editing procedure to ensues that all features that crose adjacent map sheets have the same edge location. Lines are used. When watching feature in adjacent coverage.
EGA
Enhanced Graphics Adapter. A graphics subsystem capable of 64 colors and widely used in DOS-based microcomputers. The EGA was developed in 1984 to solve the poor resolution and limited color selections of the CGA. Most game software requires EGA, but the 64-color limit is unsuitable for serious image processing. (See also: CGA, VGA.)
EISA
Extended Industry Standard Architecture. One of the standard bus architectures for microcomputers. (See also: bus.)
ELAS
A public domain, first-generation mini- and microcomputer image processing system developed by NASA at the Stennis Space Center in Slidell, LA.
elastic box
A rectangle which can be moved or resized with the mouse. Elastic boxes are used to select areas on the display monitor in processes like measuring and drawing.
elastic circle
A circle which can be moved or resized with the mouse. Elastic circles are used to select circular areas on the display monitor in processes like measuring and drawing.
elastic line
A line which can be moved or resized with the mouse. Elastic lines are used to draw segments on the display monitor in processes like measuring and drawing.
electromagnetic spectrum
"The entire spectrum, considered as a continuum, of all kinds of electric, magnetic, and visible radiation, from gamma rays having a wavelength of 0.001 angstrom to long waves having a wavelength of more than 1 million km" (Random House). Remote sensing devices typically record electromagnetic bands in the region of optical light and may include the near infrared. (See also: spectral band)
electronic atlas
A HyperIndex created from maps, photos and airphotos, airvideo, and database links. The electronic equivalent of a printed atlas.
element
(CAD) Any defined shape in a CAD object. These include arc, arc wedge, arc chord, box, circle, elliptical arc wedge, elliptical arc chord, ellipse, elliptical arc, line, point, polygon, and text elements. A block inserted into another block also acts as an element at its insertion site. Unlike vector elements, individual CAD elements retain their original shape regardless of what other elements are added and where they are placed.
element
(vector) A vector object is made up of three different types of elements: 1) points, which are single coordinate pairs (or triplets) that define a point (such as a well); 2) lines, which are curvilinear strings of coordinates which define a curved line (such as a stream) and which have nodes at the ends and intersections of lines; and, 3) polygons, which are collections of lines which inscribe an area (such as a lake).
ellipsoid
1. An ellipse rotated about its shorter axis. In the context of map projections, an ellipsoid is a geometric reference surface that closely approximates the geoid. Since the geoid (that depicts the earth) is an irregular spheroid characterized by polar flattening (or ellipticity), many methods have been developed to describe its ellipsoidal deviations. Cartographers have a selection of ellipsoids from which to choose; most of which have "best-fit" properties for certain portions of the globe. In 1924, an International ellipsoid was defined which described the earth ellipsoid as a flattening of 1 part in 297. Historically, ellipsoids were derived from careful surface measurements. More recently, satellite data has been used to construct ellipsoid models that relate coordinate measurements to the earth's center of mass. A few common standards: GRS 1980 (North America), WGS 72 (NASA/satellite), Australian (Australia), Krasovsky (Soviet Union), Clarke-1880 (Africa), Clarke-1886 (North America, Philippines), Airy (Great Britain), Bessel (Central Europe, Chile, Indonesia), Everest (India, Burma, Pakistan, Afghan, Thailand, and other southern Asian countries), and International (most other areas).
2. The mathematical shape that best describes the shape of the earth and yet is relatively simple to deal with mathematically ellipsoid are defined with two numbers. First the equatorial radius must be specified. This is also referred to as the semi-major axis second one of the three numbers must be given the polar radius also known as the semi-minor axis), the eccentricity, or the flattening given the equatorial radius and the any of the these secondary values, the remaining secondary values can be computed. A specific determination of the size of the earth is of the referred to as an ellipsoid. For eg, the phrase "Clarke ellipsoid of 1866" is frequently used to refer to the measurements of the size of the earth made by Clarke on 1866.
ellipsoid height
The height of on object above the reference ellipsoid in use. Now days this term is generally used to qualify an elevation as being measured from the ellipsoid as opposed to the geoid. GPS systems calculate ellipsoidal height. The geoid height at that location must be subtracted to obtain what is commonly refered to as the elevation.
EO cartridge
See: erasable optical cartridge
EO drive
See: erasable optical drive
epidemiology
The study of the various factors influencing the occurrence, distribution, prevention, and control of disease, injury, and other health related events in a defined human population.
epipolar
A condition of geometric coplanarity established between a pair of stereo images to give them the same relative orientation. Stereo images that have epipolar orientation can be used to derive a network of correlation points in preparation for DEM extraction.
EPPL7
Environmental Planning and Programming Language. A raster-based GIS system developed and sold by the State of Minnesota.
EPS
Encapsulated PostScript®.
Equal area projection
A projection that accurately preserves the area of projection. All projections introduce some distortion into the cartesian results, to a certain degree, however, the mathematics chosen can elements certain types of distortion. An equal area projection preserves the area of geodetic objects although the shape might be distorted, For eg, a circle on the surface of the earth may be converted to on elliptical shape by an Equal Area Projection, but the area covered by the ellipse will faithfully represent the area of the circle. A coin place on the map produced with an equal area projection covers the same amount of real area no matter where it is placed on the maps.
equalized histogram
A histogram whose distribution has been mathematically adjusted so as to come as close as possible to having an equal number of cells of each data value.
Equidistant Projection
A projection that accurately preserves the distance between certain objects. All projections introduce some distraction into the cartesian results, to a certain degree, however the mathematics chosen can eleminate certain type of distortions while introducing other type of distortion. An equidistant projection preserves the distance of all points to a specific point, such as the origin of the co-ordinate system, or preserve the court distance between all points on the same meridian.
Equireal Projection
A term rarely used to qualify a projection as having the equal area characteristic.
Equirectangular Projection
Another name used to refer equidistant cylindrical projection.
erasable optical cartridge or EO cartridge
A two-sided removable storage unit that typically holds between 300 and 500 megabytes per side. Data on EO cartridges can be erased so the cartridge can be updated or re-used.
erasable optical drive or EO drive
A 5 1/4" high capacity storage device that uses removable double-sided cartridges which typically store between 300 and 500 megabytes per side. EO drives are similar to WORM drives, with the difference that EO cartridges can be erased and re-used, while data on WORM disks is permanent and cannot be erased. (See also: WORM drive.)
ERDAS
Earth Resources Data Analysis System. A first-generation, raster-oriented microcomputer image processing and GIS system marketed by ERDAS, Inc.
escape code
A code which controls the format of text output. SML supports a set of common escape codes: \t (tab), \b (backspace), \n (newline), \<carriage return> (line continuation: the "stitch" character), and \\ (the '\' character).
euclidean distance
The shortest distance between two points in feature space, calculated using the Pythagorean theorem.
exabyte, Ebyte, or Eb
A computer unit of measurement for (approximately) 1,000,000,000,000,000,000 bytes, 1,000,000,000,000,000 kilobytes, 1,000,000,000,000 megabytes, 1,000,000,000 gigabytes, 1,000,000 terabytes, or 1000 pecabytes. (See also: bit, byte, gigabyte, kilobyte, megabyte, pecabyte, terabyte)
expansion slot
A socket for an optional circuit card on the main circuit board of a microcomputer (the motherboard).
explicit destruction
When a user action has irreversible or negative consequences, the process requires the user to take explicit action and to confirm that intent by responding to an appropriate warning message, such as "Are you sure you want to delete selected items?" before destruction is performed.
exporting vector or raster objects
Exporting an object from a project file converts it to a format recognized by other image processing or GIS software. Color schemes; arc, node, and polygon structure; geographic calibration; and any other supporting data used in the target format is included.
expression
(in database queries) A line in a query that compares values. An expression evaluates to "true" (1) or "false" (0). Example: numlines < 3. It compares the numlines variable for the current node element with the number 3. The expression is true only if the value of numlines is less than three. Also, an expression can evaluate to a number (for example: 2*YIELD). If such an expression is used where true and false values are needed, 0 is treated as false, and anything else is treated as true.
external database file
A database file that has only been linked to a project file and is being maintained as a separate file. An external database file may still be processed by your database programs. (See also: database object, internal database file.)
external raster
A raster file that has only been linked to a project file and is being maintained as a separate file. An external raster 1) is stored in a DOS file, 2) follows a very simple format, and 3) is not stored internally in a project file.
extrema points
The highest and lowest points and flat areas locally as indicated by the elevation raster cell values. Extrema are change points determined by the comparison of each cell to the eight adjacent cells. A cell whose eight boundary cells are all lower than the cell is defined as a single local maximum. A cell whose eight boundary cells are all higher than the cell is defined as a single local minimum. Two or more adjacent cells with the same value whose boundary cells are all lower are defined as contiguous local maxima. Two or more adjacent cells with the same value whose boundary cells are all higher are defined as contiguous local minima. Two or more adjacent cells with the same value whose boundary cells also have the same value are defined as a flat area.
easting
A rectangular (x,y) coordinate measurement of distance east from a north-south reference line, usually a meridian used as the axis of origin within a map zone or projection. False easting is an adjustment constant added to coordinate values to eliminate negative numbers.
edge conditions
In agricultural row crop imagery, the biomass values for cells in the middle of a healthy row are high, while the thin plant fringes or bare soil between rows have low biomass values. Low biomass values along the edges of healthy rows are normal and are no cause for concern. But edges cannot be distinguished by value alone from the low biomass values of regions of insect or disease damage which must be identified and given special attention.
EGA
Enhanced Graphics Adapter. A graphics subsystem capable of 64 colors and widely used in DOS-based microcomputers. The EGA was developed in 1984 to solve the poor resolution and limited color selections of the CGA. Most game software requires EGA, but the 64-color limit is unsuitable for serious image processing. (See also: CGA, VGA.)
EISA
Extended Industry Standard Architecture. One of the standard bus architectures for microcomputers. (See also: bus.)
ELAS
A public domain, first-generation mini- and microcomputer image processing system developed by NASA at the Stennis Space Center in Slidell, LA.
elastic box
A rectangle which can be moved or resized with the mouse. Elastic boxes are used to select areas on the display monitor in processes like measuring and drawing.
elastic circle
A circle which can be moved or resized with the mouse. Elastic circles are used to select circular areas on the display monitor in processes like measuring and drawing.
elastic line
A line which can be moved or resized with the mouse. Elastic lines are used to draw segments on the display monitor in processes like measuring and drawing.
electromagnetic spectrum
"The entire spectrum, considered as a continuum, of all kinds of electric, magnetic, and visible radiation, from gamma rays having a wavelength of 0.001 angstrom to long waves having a wavelength of more than 1 million km" (Random House). Remote sensing devices typically record electromagnetic bands in the region of optical light and may include the near infrared. (See also: spectral band)
electronic atlas
A HyperIndex created from maps, photos and airphotos, airvideo, and database links. The electronic equivalent of a printed atlas.
element
(CAD) Any defined shape in a CAD object. These include arc, arc wedge, arc chord, box, circle, elliptical arc wedge, elliptical arc chord, ellipse, elliptical arc, line, point, polygon, and text elements. A block inserted into another block also acts as an element at its insertion site. Unlike vector elements, individual CAD elements retain their original shape regardless of what other elements are added and where they are placed.
element
(vector) A vector object is made up of three different types of elements: 1) points, which are single coordinate pairs (or triplets) that define a point (such as a well); 2) lines, which are curvilinear strings of coordinates which define a curved line (such as a stream) and which have nodes at the ends and intersections of lines; and, 3) polygons, which are collections of lines which inscribe an area (such as a lake).
ellipsoid
An ellipse rotated about its shorter axis. In the context of map projections, an ellipsoid is a geometric reference surface that closely approximates the geoid. Since the geoid (that depicts the earth) is an irregular spheroid characterized by polar flattening (or ellipticity), many methods have been developed to describe its ellipsoidal deviations. Cartographers have a selection of ellipsoids from which to choose; most of which have "best-fit" properties for certain portions of the globe. In 1924, an International ellipsoid was defined which described the earth ellipsoid as a flattening of 1 part in 297. Historically, ellipsoids were derived from careful surface measurements. More recently, satellite data has been used to construct ellipsoid models that relate coordinate measurements to the earth's center of mass. A few common standards: GRS 1980 (North America), WGS 72 (NASA/satellite), Australian (Australia), Krasovsky (Soviet Union), Clarke-1880 (Africa), Clarke-1886 (North America, Philippines), Airy (Great Britain), Bessel (Central Europe, Chile, Indonesia), Everest (India, Burma, Pakistan, Afghan, Thailand, and other southern Asian countries), and International (most other areas).
EO cartridge
See: erasable optical cartridge
EO drive
See: erasable optical drive
epidemiology
The study of the various factors influencing the occurrence, distribution, prevention, and control of disease, injury, and other health related events in a defined human population.
epipolar
A condition of geometric coplanarity established between a pair of stereo images to give them the same relative orientation. Stereo images that have epipolar orientation can be used to derive a network of correlation points in preparation for DEM extraction.
EPPL7
Environmental Planning and Programming Language. A raster-based GIS system developed and sold by the State of Minnesota.
EPS
Encapsulated PostScript®.
equalized histogram
A histogram whose distribution has been mathematically adjusted so as to come as close as possible to having an equal number of cells of each data value.
erasable optical cartridge or EO cartridge
A two-sided removable storage unit that typically holds between 300 and 500 megabytes per side. Data on EO cartridges can be erased so the cartridge can be updated or re-used.
erasable optical drive or EO drive
A 5 1/4" high capacity storage device that uses removable double-sided cartridges which typically store between 300 and 500 megabytes per side. EO drives are similar to WORM drives, with the difference that EO cartridges can be erased and re-used, while data on WORM disks is permanent and cannot be erased. (See also: WORM drive.)
ERDAS
Earth Resources Data Analysis System. A first-generation, raster-oriented microcomputer image processing and GIS system marketed by ERDAS, Inc.
escape code
A code which controls the format of text output. SML supports a set of common escape codes: \t (tab), \b (backspace), \n (newline), \<carriage return> (line continuation: the "stitch" character), and \\ (the '\' character).
euclidean distance
The shortest distance between two points in feature space, calculated using the Pythagorean theorem.
exabyte, Ebyte, or EB
A computer unit of measurement for (approximately) 1,000,000,000,000,000,000 bytes, 1,000,000,000,000,000 kilobytes, 1,000,000,000,000 megabytes, 1,000,000,000 gigabytes, 1,000,000 terabytes, or 1000 pecabytes. (See also: bit, byte, gigabyte, kilobyte, megabyte, pecabyte, terabyte)
expansion slot
A socket for an optional circuit card on the main circuit board of a microcomputer (the motherboard).
explicit destruction
When a user action has irreversible or negative consequences, the process requires the user to take explicit action and to confirm that intent by responding to an appropriate warning message, such as "Are you sure you want to delete selected items?" before destruction is performed.
exporting vector or raster objects
Exporting an object from a project file converts it to a format recognized by other image processing or GIS software. Color schemes; arc, node, and polygon structure; geographic calibration; and any other supporting data used in the target format is included.
expression
(in database queries) A line in a query that compares values. An expression evaluates to "true" (1) or "false" (0). Example: numlines < 3. It compares the numlines variable for the current node element with the number 3. The expression is true only if the value of numlines is less than three. Also, an expression can evaluate to a number (for example: 2*YIELD). If such an expression is used where true and false values are needed, 0 is treated as false, and anything else is treated as true.
external database file
A database file that has only been linked to a project file and is being maintained as a separate file. An external database file may still be processed by your database programs. (See also: database object, internal database file.)
external raster
A raster file that has only been linked to a project file and is being maintained as a separate file. An external raster 1) is stored in a DOS file, 2) follows a very simple format, and 3) is not stored internally in a project file.
extrema points
The highest and lowest points and flat areas locally as indicated by the elevation raster cell values. Extrema are change points determined by the comparison of each cell to the eight adjacent cells. A cell whose eight boundary cells are all lower than the cell is defined as a single local maximum. A cell whose eight boundary cells are all higher than the cell is defined as a single local minimum. Two or more adjacent cells with the same value whose boundary cells are all lower are defined as contiguous local maxima. Two or more adjacent cells with the same value whose boundary cells are all higher are defined as contiguous local minima. Two or more adjacent cells with the same value whose boundary cells also have the same value are defined as a flat area.