Adding Grid Shift (TIFF, GSB, and GTX) Files

TerraExplorer uses GeoTIFF grid shift files to shift and transform between some coordinate systems that have different datums. For backward compatibility, GSB and GTX grid shift files are also currently supported. When the Well-Known Text (WKT) of one of the coordinate systems in your project references a particular grid shift file, TerraExplorer first checks your local computer for the file in the following locations and downloads it:

§  %AppData%\Skyline (e.g., C:\Users\[user name]\AppData\Roaming\Skyline\gdal_proj_data)

§  Proj subdirectory of installation directory (e.g., C:\Program Files\TerraExplorer\proj)

§  %ProgramData%\Skyline\gdal_proj_data (e.g., C:\ProgramData\Skyline\gdal_proj_data)

If the file was not found on your computer, TerraExplorer dynamically downloads the necessary grid shift file from the PROJ-data folder on the currently connected SkylineGlobe Server. If you are not connected to a server, the default is https://cd.proj.org. A different URL can be set in the proj.ini file found in the proj subdirectory of the installation directory. SkylineGlobe Server v8.0 and GDAL v3's coordinate system reprojection library are required for dynamic download of grid shift files. See "Use reproject by GDAL starting from version 3" in the "Using TerraExplorer Options" chapter for more information.

Grid shift files can also be preloaded for offline use, as described below.

To preload a grid shift file, find and install the missing file:

1.     Generally, when one of the coordinate systems in your project references a particular grid shift file that was not found on your computer, a notification will display in the coordinate system dialog or in the Error/Message Log with a link to a page with the required grid shift file. The grid shift file on this page is packaged as a TEZ, a TerraExplorer zip file that enables the grid shift file to be installed without manually copying the file into a specific folder. In this case, download the TEZ and then simply double-click the file to install. See "Package Grid Shift Files" in the "Working with Tools" chapter for more information. TerraExplorer will save the grid shift file to %ProgramData%\Skyline\gdal_proj_data (e.g., C:\ProgramData\Skyline\gdal_proj_data). If TerraExplorer is unable to save to that folder, it will save to %AppData%\Skyline\gdal_proj_data (e.g., C:\Users\[user name]\AppData\Roaming\Skyline\gdal_proj_data).

2.     If no TEZ was made available to you with the missing grid shift file, see the following page with download links to many common grid shift files. Download the required zip file and extract the grid shift file to %ProgramData%\Skyline\gdal_proj_data (e.g., C:\ProgramData\Skyline\gdal_proj_data). If you do not have the necessary permissions to copy to this path, you can also copy the grid shift file to either of the following directories:

§  %AppData%\Skyline (e.g., C:\Users\[user name]\AppData\Roaming\Skyline\gdal_proj_data)

§  Proj subdirectory of installation directory (C:\Program Files\TerraExplorer\proj)

Note:        Additional common grid shift 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 grid shift file is missing in the VERT_CS section of the WKT, determine what grid shift file is required, and do the following:

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

EXTENSION["PROJ4_GRIDS","[Name of Grid Shift File]"

E.g.,

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

   PROJCS["RGF93 / Lambert-93",

   ...,

   AUTHORITY["EPSG","2154"]],

VERT_CS["NGF-IGN69 height",

   VERT_DATUM["Nivellement General de la France - IGN69",2005,

         EXTENSION["PROJ4_GRIDS","RAF18.gtx"],

   AUTHORITY["EPSG","5119"]],

   UNIT["metre",1,AUTHORITY["EPSG","9001"]],

   AXIS["Up",UP],AUTHORITY["EPSG","5720"]]

]

2.     Find and install the missing grid shift file as described above.