Projection Definition File

Orbit supports the Well Known Text Projection definition file (*.prj) as defined by the OGC, see OGC PRJ-WKT definition.
A PRJ file is a single line plain text file describing the coordinate system, its datum and, if applicable, the projection.

Orbit supports the WKT PRJ file as defined by the OGC. Other PRJ variants aren't supported by Orbit.

The OGC definition includes the TOWGS84 datum transformation parameters. The units of these 7 parameters are (meter,meter,meter,arc-sec,arc-sec,arc-sec,parts-per-million). The signs of the angles should be as the EPSG “Position Vector 7-parameter transformation” method (code 9606), not the “Coordinate Frame Rotation” method (code 9607).

More information see :

• Spatialreference.org
• OGC Coordinate Transformation Service > 7.3.18 TOWGS84
• EPSG Guidance Note 7-2

Prj files can be added as custom Orbit system CRS definition. A custom system CRS can be used to define the dataset CRS, see Coordinate Reference Systems.

A lot of pre-defined Coordinate Reference Systems and Coordinate Transformations are accessible through the Orbit Software by using the EPSG Geodetic Parameter Dataset. However, the EPSG database does not record all possible geodetic parameters in use around the world. In addition to the pre-defined CRS in the EPSG database, one can create custom CRS definitions by creating a custom PRJ-file.

Create and edit these files using a text editor. Take care of spelling and file syntax.
To use a PRJ file as custom CRS in Orbit, the prj should not refer to a by Orbit supported EPSG Projection Authority. Other Authority settings do not need to be removed. In the example below “AUTHORITY[“EPSG”,”31370“],” should be removed.

http://spatialreference.org/ref/epsg/31370/

As it is :

PROJCS["Belge1972 / Belgian72",GEOGCS["Belge1972",DATUM["Reseau_National_Belge_1972",SPHEROID["International1924",6378388,297,AUTHORITY["EPSG","7022"]],TOWGS84[106.869,-52.2978,103.724,-0.33657,0.456955,-1.84218,1],AUTHORITY["EPSG","6313"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4313"]],UNIT["metre",1,AUTHORITY["EPSG","9001"]],PROJECTION["Lambert_Conformal_Conic_2SP"],PARAMETER["standard_parallel_1",51.16666723333333],PARAMETER["standard_parallel_2",49.8333339],PARAMETER["latitude_of_origin",90],PARAMETER["central_meridian",4.367486666666666],PARAMETER["false_easting",150000.013],PARAMETER["false_northing",5400088.438],AUTHORITY["EPSG","31370"],AXIS["X",EAST],AXIS["Y",NORTH]]

Just to read more easily :

PROJCS["Belge 1972 / Belgian 72",
GEOGCS
[
    "Belge 1972",
    DATUM
    [
        "Reseau_National_Belge_1972",
        SPHEROID["International 1924",6378388,297,AUTHORITY["EPSG","7022"]],
        TOWGS84[106.869,-52.2978,103.724,-0.33657,0.456955,-1.84218,1],
        AUTHORITY["EPSG","6313"]
    ],
    PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],
    AUTHORITY["EPSG","4313"]
],
UNIT["metre",1,AUTHORITY["EPSG","9001"]],
PROJECTION["Lambert_Conformal_Conic_2SP"],
PARAMETER["standard_parallel_1",51.16666723333333],
PARAMETER["standard_parallel_2",49.8333339],
PARAMETER["latitude_of_origin",90],
PARAMETER["central_meridian",4.367486666666666],
PARAMETER["false_easting",150000.013],
PARAMETER["false_northing",5400088.438],
AUTHORITY["EPSG","31370"],
AXIS["X",EAST],
AXIS["Y",NORTH]
]