Geographic coordinate system missing


I'm currently working in a big railway project that uses a bespoke GCS.

I was following a forum post that explaining how to create a transformation. In the process the seed file "UserOverrideGeodeticTransformSeed.asc" needed to be altered.

The heading of the file contain the following text:

"# In case of absolute necessity it is possible to override the list or
# order of the grid shift files for a specific datum transformation.
# This should only be done if no other solution is available.
# Bentley Systems would be glad to introduce new files directly
# referenced by the built-in system dictionary as part of a refresh to
# its software. Contact Bentley system through the normal support channel."

As you can imagine this new GCS is a big headache with all the legacy data.

Is there anyone in the position to help?

Thank you in advance for your time.



  • According to the replies, you are working with the HS2 Survey Grid (SnakeGrid). 

    The HS2 SnakeGrid (phase 1+2a) can now be defined within the Microstation GCS library using an NTv2 transform + Transverse Mercator projection. It will be available in Microstation update 13 however will require manual installation of the transformation files.  MS CE Update 14 will have the files distributed.  

    Two GCS will be available: HS2_Snake_2002 and HS2_Snake_2015.  These are essentially the same GCS - the difference is the transformation used for conversions into other GCS:

    • Use HS2_Snake_2002(HS2TN02) when converting to/from OSTN02.BritishNatGrid 
    • Use HS2_Snake_2015(HS2TN15) when converting to/from OSTN15.BritishNatGrid
    • Use HS2_Snake_2015(HS2TN15) when converting to/from ETRS89 OS Net v2009 latitude/longitude (current OS Active Network)

    Note that the HS2TN02 transform is equivalent to using the HS2P1+14 SnakeGrid parameter file.  If converting into lat/lon using HS2TN02/HS2P1+14 then these coordinates are only compatible for use with the legacy OS Active Network (OS Net v2001).

  • Hi Jim,

    Thank you for your help on this subject.

    I'm eager to try this new solution.

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