Global Mapper v24.1

Problem with Custom Datum (7-parameters)

Hi to everybody, I'm new in the forum and I'm not an advanced user of Global Mapper. I'm using Global Mapper v21.0.0 (b091619) (23) [64-bit].

I'have some issues using a custom datum.

I have created a custom datum based on 7-parameter Bursa-Wolfe (Coordinate Frame Rotation) method (as this datum is not available in the EPSG database).

I have been provided a trial point to verify the correctness of conversion, and everything seems to work correctly. I have saved the project and I have checked that the right parameters have been stored on Global Mapper custom_datums.txt file.

The problem is that every time I go to open again the saved project, the custom datum rotation parameters changes alternately.

Also the datum name changes with an increasing suffix added to the original datum name (_##).

Please find attached two screenshot sof my custom_datums.txt file (one with datum "revision" 13 and on with "revision" 14): the datums with even number at the end of the name are the "correct" ones (i.e. according to the original custom datum). Furthermore, please note that the previous datum revisions remain in the custom_datums.txt file but the rotation parameters have been deleted.

Probably I did something wrong or it is a known bug of my release?

Please, in your opinion there is a way to solve this problem.

Thanks in advance



  • Sorry for my English. Why don't you save your GRS parameters in a .prj- file?

  • tikhpetr, I thank you for your comment and I apologize for my delay in responding.

    I undestand that the standard .prj files generally does not contain the datum transformation parameters (at least according to my Global Mapper version; I don't know if in the latest version something has changed).

    The custom datum transformation parameters (from local datum to WGS84) are instead stored in the above mentioned custom_datums.txt file.

    Just a clarification about my original post.

    I forgot to mention that I'm working in the local (custom) datum. The problem will not exist if all my data will be georeferenced according to the local datum. However, I have to share data with other teams which are working in a different reference systems (generally WGS84). Thus, every day I have to perform datum tranformations to import data from WGS84 and export to WGS84.

    For this reason it is important for me that the transformation parameters work correctly but unfortunately this is not my case.

    Everytime I open my workspace, before doing anything I have to check that the datum parameters are correct (and in case not, I have to save, close and open again the workspace): this way of working is getting exasperating. 😓

    That's why I'd like to know if I'm doing something wrong.

  • My English is very bad, and I have prepared for you screens. Take the archive with them from here:

  • This is about saving the datum in the format .prj and saving the transition parameters to WGS 84.

    God willing, this will help.