Coordinate system definition format

The coordinate system is defined in the coordinate system definition file using the following format:

code description REF_FRAME ref_frame_code type
              [proj_definition] [RANGE extents]

In this definition the square brackets denote optional components. The components of the definition are:

code is an identifier for the coordinate system. This may contain letters, numbers, and the underscore character. It cannot contain blanks. It is used in SNAP coordinate files to specify which coordinate system to use. Aliases for the code can be included using "=" to separate the codes, for example "NZGD2000=NZGD2000_20170601".

description is a quoted text description of the reference frame

ref_frame_code is the code for the reference associated with the reference frame. This code must have been defined in an earlier [reference frames] section of the file.

type is the type of coordinate system. This can be one of GEOCENTRIC, GEODETIC, or PROJECTION

proj_definition is the projection definition. It is only defined for projection coordinate systems. The contents of this definition depends upon the type of the definition.

extents optionally defines the range of coordinates over which the projection is valid. This is detailed below.

The coordinate system definition may optionally be followed by a range defining valid values for coordinates. This does not apply for geocentric systems. For geodetic systems the range defines the minimum and maximum latitudes and longitudes of the coordinates in decimal degrees. The format is

RANGE min_long min_lat max_long max_lat

For projection coordinate systems the range defines the minimum and maximum values of the easting and northing, formatted as

RANGE min_easting min_northing max_easting max_northing

The following example shows a geocentric and a geodetic coordinate system definition.

[coordinate_systems]
WGS84_XYZ  "World Geodetic System 1984 - XYZ" REF_FRAME WGS84 GEOCENTRIC
NZGD49 "New Zealand Geodetic Datum 1949" REF_FRAME NZGD49 GEODETIC

The following projection coordinate systems are supported:

New Zealand Map Grid

Transverse Mercator projection

Equatorial Mercator projection

Lambert Conformal Conic projection

Polar Stereographic projection

Gnomic projection