Projection Parameters

Producer Field Guide

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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.

Choice of the projection to be used depends upon the desired major property and the region to be mapped. After choosing the desired map projection, you define several parameters. These parameters fall into three general classes:

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

Depending upon the selected projection type, one or more additional options are shown for setting projection parameters.

Spheroid Name    Name of the spheroid used.

Spheroid Axis    Length in meters of the semi-major axis and semi-minor axis of the spheroid used.

Datum Name    Name of the datum used.

Datum Grid    Name of the datum grid shift file if used, which contains parameters to transform coordinates from one datum to another.

Datum Parameters    Datum parameters, if a parametric datum is used.

Scale factor at central meridian    Modifies the scale distortion. A value of one indicates true scale only along the central meridian. A factor of less than, but close to one is often used.

Longitude of central meridian    Defines the degrees of longitude of the central meridian.

Latitude of origin of projection    Defines the line of latitude (parallel) of the origin of the map projection.

False easting    A value applied to the easting coordinate to prevent negative values when moving west from the central meridian. Easting coordinate for a feature is the distance in meters east or west of the central meridian.

False northing    A value applied to the northing coordinate to prevent negative values when moving south from the latitude of origin. Northing coordinate for a feature is the distance in meters north or south of the latitude of origin.

Latitude of 1st standard parallel    First line of latitude (parallel) used as control lines in the computation of a map projection. The first standard parallel is the southernmost.

Latitude of 2nd standard parallel    Second line of latitude (parallel) used as control lines in the computation of a map projection, used with a first standard parallel.

Longitude of center of projection    Longitude of the center of the projection.

Latitude of center of projection    Latitude of the center of the projection.

UTM Zone    If the Projection Type is UTM, shows the UTM Zone number.

NORTH or SOUTH    If the Projection Type is UTM, shows whether the projection is North or South.

State Plane Zone    If the Projection Type is State Plane, shows the State Plane Zone number.

Zone Type    If the Projection Type is State Plane, shows the zone type.

NAD    If the Projection Type is State Plane and uses a North American Datum, specifies which datum is used.