Adding Vertical Datum (GTX) Files

SkylineGlobe Server uses vertical datum grid shift files (GTX) for shifting and transforming between some coordinate systems that have different datums, e.g., when streaming mesh layers as 3D Tiles to Cesium clients, they are streamed in ECEF coordinate system and their elevation values are reprojected. Sometimes the Well-Known Text (WKT) of a layer’s coordinate system references a particular GTX file that was not bundled with your installation, or the reference itself is missing from the WKT. The steps below describe how to add the missing GTX information in both of these cases.

To add missing GTX information:

1. Generally, when one of your layers' coordinate systems references a particular GTX file that was not found on your computer, a notification will display in SGS Manager's Messages page with a link to a page with the required GTX file. See “Searching and Viewing Messages” in the Monitoring SkylineGlobe Server chapter. Save the GTX to the SGS bin folder that is placed under the SGS installation (by default C:\inetpub\wwwroot\SG).

2. If no GTX was made available to you, see the following page with download links to many common GTX files. Download the required zip file and extract the GTX to the SGS bin folder that is under the SGS installation (by default C:\inetpub\wwwroot\SG).
Note: Additional common GTX files are available from the following websites:

§ https://github.com/OSGeo/proj-datumgrid/tree/master/

§ https://vdatum.noaa.gov/download.php

§ https://raw.githubusercontent.com/OSGeo/proj.4/gh-pages/proj.pdf

§ https://proj.org/resource_files.html#transformation-grids

If a reference to the GTX file is missing in the VERT_CS section of the WKT, determine what GTX file is required, and do the following:

1. Add a reference to the required GTX within the WKT's VERT_DATUM object that is under the VERT_CS object:

EXTENSION["PROJ4_GRIDS","[Name of GTX File]"

E.g.,

COMPD_CS["RGF93 / Lambert-93 + NGF-IGN69 height",

PROJCS["RGF93 / Lambert-93",

...,

AUTHORITY["EPSG","2154"]],