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How to define a grid based datum transformation (using .gsb file)

by jmorris ‎04-18-2017 02:17 PM - edited ‎05-14-2018 12:04 PM (1,252 Views)

Note: The workflow below is for GeoMedia versions prior to 16.5. In GeoMedia version 16.5 the root coordinate system folder path has changed to C:\Program Files (x86)\Common Files\Intergraph\GeoMedia\Program\PrivateAssemblies\Config

Therefore if using GeoMedia version 16.5 or later, please substitute the new folder path above for the path of C:\Program Files (x86)\Common Files\Intergraph\Coordinate Systems shown in the steps below.

 

To define a grid-based datum transformation in GeoMedia using a NTv2 binary grid file (.gsb) there are two steps required as shown below…

 

1. Copy the binary grid file (.gsb) to the C:\Program Files (x86)\Common Files\Intergraph\Coordinate Systems\3.0\Config\Canada folder (or equivalent folder location on your operating system).

 

2. Edit the autodt.ini file in the C:\Program Files (x86)\Common Files\Intergraph\Coordinate Systems\3.0\Config folder to add an entry for the specific datum transformation that uses the grid file.

 

For example to add a grid based datum transformation using the BETA2007.gsb file for transformations between the DHDN and ETRS89 datum you would perform the steps below.

 

1. Download the BETA2007.gsb file. The BETA2007.gsb file is available for download from…http://crs.bkg.bund.de/crseu/crs/descrtrans/BeTA/de_dhdn2etrs_beta.php

 

2. Copy the BETA2007.gsb file to the folder…

C:\Program Files (x86)\Common Files\Intergraph\Coordinate Systems\3.0\Config\Canada

... or the equivalent Common Files\Intergraph\Coordinate Systems\3.0\Config\Canada folder on your operating system.

 

3. Make a backup copy of the autodt.ini file in the folder... 

C:\Program Files (x86)\Common Files\Intergraph\Coordinate Systems\3.0\Config

 

4. Edit the autodt.ini file to add an entry for the transformation between the datum ETSR89 and DHDN using the BETA2007.gsb file. The format of the comma delimited autodt.ini entry is…

 

source horizontal datum name, source vertical datum name, target horizontal datum name, target vertical datum name, transformation method name, binary grid file name

 

If using the GeoMedia default vertical datum of EGM96 the new entry for our example would be…

 

csgdDeutscheHauptdreiecksnetz,csvdEGM,csgdETRS89,csvdEGM,csdtCanadianNational,BETA2007.gsb

 

A description of each of the comma delimited parameters used in this autodt.ini entry is shown below...

 

csgdDeutscheHauptdreiecksnetz – the source horizontal datum (DHDN)

csvdEGM – the source vertical datum (EGM96)

csgdETRS89 – the target horizontal datum (ETRS89)

csvdEGM – the target vertical datum (EGM96)

csdtCanadianNational – the transformation method (NTv2 Grid-Based)

BETA2007.gsb – the binary grid file

 

Note: This new entry must be placed within the autodt.ini file so that it occurs before any other entries for transformations between DHDN and ETRS89. This will ensure that the grid-based transformation using the .gsb file is ‘found’ before other entries describing a DHDN to ETRS89 datum transformation.

 

The attached autodt.ini includes the example entry described in the workflow above.

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