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PRJ Files

 

 

 

 

Beginning with Version 18.2, TPC can use ESRI Projection (.prj) files to define a Coordinate Reference System.

You can find information about PRJ files at this ESRI Technical Support site.

CRS From PRJ File (1:47) - TPC can define it's CRS (Coordinate Reference System) from an ESRI Projection (PRJ) file.


PRJ Reference

You can visit http://www.spatialreference.org/ to find Coordinate Reference Systems in any number of formats, including ESRI references, including PRJ files which TPC reads.

https://vsp.pnnl.gov/help/vsample/ESRI_PRJ_File.htm


Selecting a PRJ File

Projection files, with a .prj extension, can be selected as the CRS in the Coordinate Reference System dialog. Just use the Browse button and select the file.

In the Transform Survey dialog, you can also Browse to select a .prj file.


EPSG 3857 and 4326

Google Earth, Open Street Maps, etc. generally use these coordinate reference systems which TPC provides as .prj files.

EPSG: 4326 ground coordinates

EPSG: 3857 grid coordinates

See EPSG 3857 & 4326


PROJCS

If a prj file contains PROJCS[...] data, TPC can generally create a CRS from it.


GEOGCS Only

If a prj file contains only GEOGCS[...] data, TPC is not able to createa CRS from it.  This is because it is missing the projection information like central meridian, false northing/easting, etc.

However, if TPC can identify the GEOGCS name, like "GCS_North_American_1983", TPC will try to match it to a matching CRS file.


No Zones

PRJ files define a single projection or zone. As a result, you will not find any Zone information associated with a CRS derived from a PRJ file.


Supported PRJ Data

PROJCS, GEOGCS, DATUM, SPHEROID, PRIMEM, UNIT, PROJECTION, PARAMETER, AXIS

Non-Supported PRJ Data

AUTHORITY, VERTCS, VDATUM


Units

TPC reads the PROJCS UNIT keyword to determine the units of coordinate parameters, like FALSE_EASTING.

UNIT["Meter",1] tells TPC the CRS units are meters. The choice of US Survey Foot vs Interntional Survey Foot is not determined by this UNIT settings.

UNIT["Foot_US",0.30480060960121924] tells TPC the CRS units are US Survey Feet.

UNIT["Foot",0.3048] tells TPC the CRS units are US Survey Feet.

UNIT["Feet",0.3048] tells TPC the CRS units are US Survey Feet.

UNIT["Foot_International",0.3048] tells TPC the CRS units are International Survey Feet.


PRJ Format

PROJCS["Alaska_Albers_Equal_Area_Conic",

GEOGCS["GCS_North_American_1983",

DATUM["D_North_American_1983",

SPHEROID["GRS_1980",6378137,298.257222101]

],

PRIMEM["Greenwich",0],

UNIT["Degree",0.017453292519943295]

],

PROJECTION["Albers"],

PARAMETER["False_Easting",0],

PARAMETER["False_Northing",0],

PARAMETER["central_meridian",-154],

PARAMETER["Standard_Parallel_1",55],

PARAMETER["Standard_Parallel_2",65],

PARAMETER["latitude_of_origin",50],

UNIT["Meter",1]

]

TPC converts all prj keywords to lowercase to compare them. As a result, TPC considers prj keywords to be not case sensitive. So "False_Easting" and "false_easting" are considered to the same keyword.

In practice, prj files use varied, but similar, keywords to define the same data. For example 'feet_us' and 'foot_us' both define US Survey Foot units.  'lambert_conformal_conic_2sp' and 'lambert_conformal_conic' both define a Lambert conic projection with both a North and a South latitude.

Because of this, when TPC reads a .prj file, it reports unsupported keywords in the Message View, such as 'Unsupported Keyword: "UNIT",x0.3048 dm'.  You can send this prj file to tech@traverse-pc.com and we will update TPC to include that keyword.


Related Topics

Coordinate Reference Systems
 

 

 

 

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