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Projection Definition File
Name | Projection Definition File |
Acronym | PRJ |
File Extension | *.prj |
The prj-file is a plain text file describing the the coordinate system and projection information using text format.
A prj-file can be used to define a custom Orbit Coordinate system, which can be used to define the dataset crs : Coordinate Reference Systems in Orbit
The prj-file cannot be used as direct dataset coordinate definition. A dataset coordinate definition in Orbit is saved in the Orbit Resource Description file.
Information in PRJ file
Some typical information contained in the .prj file is:
- Geographic coordinate system
- Datum
- Spheroid
- Prime meridian
- Map projection
- Latitude of origin
- Scale factor
- Central meridian
- False northing
- False easting
- Standard parallels
- Units used
PRJ Features
Format
The text is created in the WKT-format: Support of WKT is under development. Not all features are fully supported (like vertical coordinate systems or special units).
Feel free to send an email to support@orbitgis.com if your WKT file is not working as expected.
Do not forget to add the “TOWGS84” element (with seven parameters) to the “DATUM” element. See section “7.3.18 TOWGS84” of the WKT specification.
Example
PROJCS["NAD83 / Austin", \ GEOGCS["NAD83", \ DATUM["North_American_Datum_1983", \ SPHEROID["GRS 1980", 6378137.0, 298.257222101], \ TOWGS84[0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]], \ PRIMEM["Greenwich", 0.0], \ UNIT["degree", 0.017453292519943295], \ AXIS["Lon", EAST], \ AXIS["Lat", NORTH]], \ PROJECTION["Lambert_Conformal_Conic_2SP"], \ PARAMETER["central_meridian", -100.333333333333], \ PARAMETER["latitude_of_origin", 29.6666666666667], \ PARAMETER["standard_parallel_1", 31.883333333333297], \ PARAMETER["false_easting", 2296583.333333], \ PARAMETER["false_northing", 9842500.0], \ PARAMETER["standard_parallel_2", 30.1166666666667], \ UNIT["m", 1.0], \ AXIS["x", EAST], \ AXIS["y", NORTH], \ AUTHORITY["EPSG","100002"]]
Supported Projection Methods
EPSG | Projection Name |
---|---|
9812 | Hotine_Oblique_Mercator |
9819 | Krovak |
9801 | Lambert_Conformal_Conic_1SP |
9802 | Lambert_Conformal_Conic_2SP |
9803 | Lambert_Conformal_Conic_2SP_Belgium |
9802 | Lambert_Conformal_Conic |
9804 | Mercator_1SP |
9815 | Oblique_Mercator |
9809 | Oblique_Stereographic |
9807 | Transverse_Mercator |
Why use PRJ-files
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, OrbitGIS accepts custom CRS definitions by creating seperate PRJ-files.