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How to create a custom local datum transform.

Joe McPherson
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Objective:

I need to transform data between two different datums.  I have not been able to find a local datum transform from the drop list in the Coordinates System dialog box with the required transformation parameters (translation, rotation, scale).  Is it possible to add a custom local datum transform?

Resolution:

In order to create a custom local datum transform, the datumtrf.csv and ldatum.csv files in the User csv directory need to be modified. (C:\Users\{UserName}\Documents\Geosoft\Desktop Applications 9\csv)

We recommend that you make backups of these files and view the backups in Excel.  It is best to edit the original files in a text editor such as Notepad, instead of making the edits in Excel.


To edit the datumtrf.csv file:

  • In Windows Explorer navigate to C:\Users\{UserName}\Documents\Geosoft\Desktop Applications 9\csv and open the datumtrf.csv file. 
  • Datum_trf column: datum name. Enter “*” and a name for your datum (e.g. *newdatum). If this is a name listed in the EPSG (OPG) tables, the name can be entered without being preceded by “*”.
  • Code column: is used to reference an EPSG code. If you are not adding a local datum transfer that is in the EPSG tables, this item can be left blank.
  • MapInfo column: this is a MapInfo code. If it is not a local datum recognized by MapInfo, leave this item blank.
  • Area of use column: enter the area where this datum will be applied between square brackets “[ ]”, so it can be easily identified (e.g. [local]).
  • Datum column: enter the datum name exactly how it appears in the datum.csv file (e.g. WGS 84)
  • Target column: enter the datum name related with the parameters of this transform. (e.g. WGS 84)
  • dx, dy, dz columns:  vectors in meters.
  • rX, rY, rZ columns: rotation in arc-seconds.
  • Scale column: scale of correction value.

Save your edits once the information has been entered.

To edit the ldatum.csv file:

  • In Windows Explorer navigate to C:\Users\{UserName}\Documents\Geosoft\Desktop Applications 9\csv and open the ldatum.csv file. 
  • Area_of_use column:
  • Datum column:
  • Datum_trf column:
    For these 3 columns, enter exactly the same names used in datumtrf.csv file.

Save your edits once the information has been entered.

The local datum transform will now be available from the Coordinate System dialog box in your Geosoft application

Notes:

It is important that  you do not edit the csv files in C:\Program Files\Geosoft\{program}\csv. Only edit the csv files in the user folder (C:\Users\{UserName}\Documents\Geosoft\Desktop Applications 9\csv)

In earlier versions of our applications the user csv files where located C:\Program Files\Geosoft\{program}\user\csv. 

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