# Available Map Projections

## Producer Field Guide

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In ERDAS IMAGINE, map projection information appears in Projection Chooser, used to georeference images and to convert map coordinates from one type of projection to another. The Projection Chooser provides all of the supported map projections. The projections listed in the referenced topic are some of the commonly used projections.

See Map Projections for a list and descriptions of specific map projections.

Choice of the projection to be used depends upon the desired major property and the region to be mapped (see Projection Parameters Table). After choosing the desired map projection, several parameters are required for its definition (see Uses of Common Map Projections Table). These parameters fall into three general classes:

• definition of the spheroid
• definition of the surface viewing window
• definition of scale

For each map projection, a menu of spheroids displays, along with appropriate prompts for specifying these parameters.

Units of Measure

Use the units of measure that are appropriate for the map projection type.

• Geographic coordinates are expressed in decimal degrees. When prompted, you can use the DD function to convert coordinates in degrees, minutes, seconds format to decimal. For example, for 30°51’12’’:

dd(30,51,12) = 30.85333

-dd(30,51,12) = -30.85333

or

30:51:12 = 30.85333

You can also enter Geographic coordinates in radians.

• State Plane coordinates are expressed in feet or meters.
• All other coordinates are expressed in meters.

Note also that values for longitude west of Greenwich, England, and values for latitude south of the equator are to be entered as negatives.

See Units of Measure in Help for definitions and formulas to convert units of measure for angles, distance, area, volume, and time.

Uses of Common Map Projections Table

 Type Map projection Construction Property Use 0 Geographic N/A N/A Data entry, spherical coordinates 1 Universal Transverse Mercator Cylinder (see #9) Conformal Data entry, plane coordinates 2 State Plane (see #4,7,9,20) Conformal Data entry, plane coordinates 3 Albers Conical Equal Area Cone Equivalent Middle latitudes, E-W expanses 4 Lambert Conformal Conic Cone Conformal True Direction Middle latitudes, E-W expanses flight (straight great circles) 5 Mercator Cylinder Conformal True Direction Nonpolar regions, navigation (straight rhumb lines) 6 Polar Stereographic Plane Conformal Polar regions 7 Polyconic Cone Compromise N-S expanses 8 Equidistant Conic Cone Equidistant Middle latitudes, E-W expanses 9 Transverse Mercator Cylinder Conformal N-S expanses 10 Stereographic Plane Conformal Hemispheres, continents 11 Lambert Azimuthal Equal Area Plane Equivalent Square or round expanses 12 Azimuthal Equidistant Plane Equidistant Polar regions, radio/seismic work (straight great circles) 13 Gnomonic Plane Compromise Navigation, seismic work (straight great circles) 14 Orthographic Plane Compromise Globes, pictorial 15 General Vertical Near-Side Perspective Plane Compromise Hemispheres or less 16 Sinusoidal Pseudo-Cylinder Equivalent N-S expanses or equatorial regions 17 Equirectangular Cylinder Compromise City maps, computer plotting (simplistic) 18 Miller Cylindrical Cylinder Compromise World maps 19 Van der Grinten I N/A Compromise World maps 20 Oblique Mercator Cylinder Conformal Oblique expanses (for example, Hawaiian islands), satellite tracking 21 Space Oblique Mercator Cylinder Conformal Mapping of Landsat imagery 22 Modified Transverse Mercator Cylinder Conformal Alaska

In Projection Parameters Table numbers are used for reference only and correspond to the numbers used in Uses of Common Map Projections Table. Parameters for definition of map projection types 0-2 are not applicable and are described in the text.

For Projection types 8, 20, and 21, additional parameters required for definition of the map projection are described in the text of Map Projections.

Projection Parameters Table

 Projection type (#) Parameter 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Definition of Spheroid Spheroid selections • • • • • • • • • • • • • • • • • • • Definition of Surface Viewing Window False easting • • • • • • • • • • • • • • • • • • • • False northing • • • • • • • • • • • • • • • • • • • • Longitude of central meridian • • • • • • • • • • Latitude of origin of projection • • • • • • Longitude of center of projection • • • • • • Latitude of center of projection • • • • • • Latitude of first standard parallel • • • Latitude of second standard parallel • • • Latitude of true scale • • Longitude below pole • Definition of Scale Scale factor at central meridian • Height of perspective point above sphere • Scale factor at center of projection •