Adding Grid Shift (GTX, GSB) Files

PhotoMesh uses grid shift files (GTX, GSB) for shifting and transforming between some coordinate systems that have different datums. Sometimes the Well-Known Text (WKT) of one of the coordinate systems in your project references a particular grid shift 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 grid shift information in both of these cases.

Note:    Grid shift files can be automatically installed during the PhotoMesh installation process by placing a zip file that includes the required files next to the PhotoMesh.exe file in the installation folder. See "Installing PhotoMesh" in the "Getting Started" chapter for more information.

To add a grid shift file that was not found on your computer, 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 file, packaged as a zip file. Download the required zip file.

2.     If no zip was made available to you with the missing grid shift file, you can download the required file from one of the following websites with download links to many common grid shift files:

§  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

3.     Extract the grid shift file to both the following directories for computers with full PhotoMesh installation, and to only the second directory for computers with only fuser installation:

§  The \PhotoMesh\proj subdirectory of PhotoMesh's installation directory.

§  The \PhotoMesh\Fuser\proj subdirectory of PhotoMesh's installation directory.

4.     If a reference to the grid shift file is missing in the WKT, add the following reference 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"]]

]