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.
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.
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 International 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.
East vs West Central Meridian
TPC considers a positive (+) longitude to be West and negative (-) to be East. This may or may not conform to the convention used in a particular prj file. If you use a prj file for a survey's CRS and the sign of the Central Meridian is wrong, you survey coordinates will be way off from where they should be.
In the example shown above, PARAMETER["central_meridian",-154], the central meridian is negative, which TPC would consider to be East, but since this is an Alaska projection, it should be West.
To accommodate this, TPC provides 2 methods to remove this ambiguity
Append E or W to a positive longitude
Append an E or W to the central meridian in the prj file. In the example above, this would look like PARAMETER["central_meridian",154W].
Edit the prj file if prompted
Beginning with TPC 2024, if TPC reads a prj file that does not use E or W designators for central meridians, TPC will prompt you to confirm that the sign (direction) of the central meridian value is correct.
You can use the [Preview] button to open the prj file in a word processor and change PARAMETER["central_meridian",-154] to PARAMETER["central_meridian",154] or PARAMETER["central_meridian",154W].
