I am trying to create a custom NTv2 transformation file that later on I can use to create a custom transformation for ArcGIS Pro. I have all the grid shift information in a file with the extension .grt which I can view and edit as plain text. I tried to create a grid shift ascii file (.gsa) using the information provided in my file and following the steps from the documentation and using the ntv2_file tool from here:
GitHub - Esri/ntv2-file-routines: Documentation for NTv2 files and a C API to access them
The problem is that my output .gsb file doesn't contain the grid shift values that I entered in the grid shift ascii file. Instead when I convert back the file from .gsb to .gsa I get a default value (-431602080.0) for each row and column... And I think this is either because my input grid shift ascii file isn't valid or there is a bug in the ntv2_file tool. But probably someone would have noticed it already... and I don't think it is the case.
The information that I modified in the header was read and written correctly by the ntv2_file tool, both from .gsa to .gsb and from .gsb to .gsa. The problem is only with the shifted grid values...
Is there a method or a tool for writing grid shift ascii files or do you simply edit them as normal text files and after that convert them into grid shift binary files? Is there another solution aside from the one from GitHub - Esri for creating grid shift binary files?
Thank you very much for your help,
Have you tried the -v switch on ntv2_file on command line to validate the file?