Define Global Coordinate Systems in Civil 3D…

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Looking into the eyes of a PRJ file (found with other shape file content):

PROJCS["Lambert_Conformal_Conic",GEOGCS["GCS_Geographic Coordinate System",DATUM["D_NAD83",SPHEROID["GRS_1980",6378137,298.2572220960423]]
,PRIMEM["Greenwich",0]
,UNIT["Degree",0.017453292519943295]]
,PROJECTION["Lambert_Conformal_Conic"]
,PARAMETER["scale_factor",1]
,PARAMETER["standard_parallel_1",34.91666666669978]
,PARAMETER["standard_parallel_2",27.41666666669978]
,PARAMETER["central_meridian",-100]
,PARAMETER["latitude_of_origin",31.16666666669978]
,PARAMETER["false_easting",1000000]
,PARAMETER["false_northing",1000000]
,UNIT["Meter",1]]

Have you ever discovered while reprojecting geospatial data, that selecting the assumed correct coordinate system can be a challenge but then to further discover it doesn’t exist, well that’s what blogs are for. Although Civil 3D provides us a library of coordinate systems to select from, we may need to define new coordinate systems.

imageIn Civil 3D, you can define a global coordinate system from Map 3D functionality within the program. By changing your Workspace to Tool-Based Geospatial, from the Ribbon select the Map Setup tab and within the Coordinate System panel click on Define Global Coordinate Systems… button.

Choose a category that closely resembles  the location of your new coordinate system and select the Define… button. In the General tab, enter a Code and Description then match up the PRJ file details to determine the Units and Coordinate System Type. In my case, Units  are set to Meter, Coordinate System Type set to Geodetic and the Datum set to NAD 1983, Alaska, Canada, Continental US…

Now for  the trickiest part, at least in my opinion, select the Projection tab and review the PRJ file once again.  From Civil 3D, select the Projection to Lambert Conformal Conic, double standard parallel which will configure appropriate Projection Parameters to be filled in. Deciphering terminology between Civil 3D’s Projection parameters to a PRJ file, I found, confusing but we are getting closer to unlocking its secret. False Origins values are easily located within the PRJ file but here is the trick to matching up the rest of the values:

PRJ file (part of the shape contents) Projection Parameters (C3D)
latitude_of_origin Origin latitude
central_meridian Origin Longitude
standard_parallel_1 Northern standard parallel
standard_parallel_2 Southern standard parallel

I hope this brought insight to the subject and prepares you for what you need to have prior to defining a new coordinate system. Most important, how to match it up!!

Ryan Caudell

Total CAD Systems, Inc.

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