Make custom Shift Grid

Hello,

I ´ve got one question.

I would like to make my own shift grid for national conversion between new an old datum (and reverse). I ´ve got an xls file with X, Y coordinates and their dX and dY. Is there any chance to make own shift grid in Bentley map or I will need other software.

I have read something about GSB files in GeoCoordinateData (http://communities.bentley.com/products/geospatial/desktop/f/5924/p/53164/123488#123488) but I don't  know if those files uses same values (X,Y,dX,dY) or they are completely different.

  • Rybovic,

    Bentley System does not provide any software to generate grid shift files however we do provide ways to use a datum given you have a grid shift file in the Canadian National Transformation v2 (GSB) format. I know that this format relies on variable precision cells to apply latitude and longitude deltas so it is more complex than a simple table. You may want to search over the web about the details concerning this format or contact someone at the NRC/RNC (National Resources Canada/Ressources Naturelles Canada) to obtain details about the file format (We use a third party software to read these files so we do not know the details).
    Given you succeed in generating a GSB file then to use it you must make use of the datum named GENGRID (available on latest versions of Microstation SS3 and more recent only) and follow the instructions contained in the GenGridToWgs84.gdc file located in the GeoCoordinateData directory in the Microstation path to set it up.

    Hope this helps

  • Hi,

    out of curiosity I tried to search Internet and it seems CNT v2 format seems to be very well hidden secret. Even if I found some link promising format description, a target document did not exist :-(

    Probably the only tool I found, which seems be able to create gsb format, is this tool hosted on GitHub. Readme provides good overview of the situation, but it seems even with such tool it's quite a lot of work to prepare source data to be converted to binary gsb format.

    With regards,

      Jan

  • Dear Jan and Alain,

    Thank you very much for quick answer. I had the same problem with internet searching as Jan. I did not find any relevant information about gsb files at all. Now I know what will be my next steps.
    But to be sure for 100 percent I would like to know if gsb is only way how to make shift grid. I also saw som other files in GeoCoordinateData directory.
  • Stefan,

    Although there are other formats all of which are proprietary, the NTv2 format is definitely the one almost everyone is adopting. Even countries such as Japan that used to have their own format and files are in the process of migrating to NTv2. This is the reason we only support the GENGRID datum based upon NTv2 (GSB) files. It is definitely the format I would select if I had grid shift files to build.

  • Hi Štefan,

    Unknown said:
    But to be sure for 100 percent I would like to know if gsb is only way how to make shift grid.

    In my opinion two different answers exist:

    • If you want to create own shift grid, so you will be able to set it as GCS function, gsb is the only way.
    • If you want to be able to make a simple conversion of active file between JTSK and JTSK03, which I suppose is minor coordinates change (have not checked Excel file yet), maybe it will be easier to write own macro.

    In my opinion the second way is less risky, because to the first one require to invest a time to learn about gsb format, how to use existing conversion tools, if Excel source data can be used directly etc. On the other hand a benefit of the first option is it's fully compatible with GCS engine, so it should work probably also with references.

    With regards,

      Jan