Vertical datum conversion CGVD28 to CGVD2013

[joual.f...@gmail.com]

Hello, I'm trying to convert lidar files originally from EPSG 2950 (MTM CSRS-08) with vertical datum CGVD28 to a new file with a vertical datum CGVD2013. I want to install the grid to transform the file in Z value. It seems I need a .gtx file. How, or where should I get the .gtx file? Is there a link for Quebec territory transformation .gtx grid file? Or Canadian territory transformation grid? Thanks, Frank.

[Michael Perdue]

Hello,

Assuming you have the CGVD28 -> CGVD2013 byn file, you can convert it to a GTX file with GDAL and the command:

gdal_translate -f GTX somefile.byn somefile.gtx

Cheers,

Mike

On Mon, Mar 10, 2025 at 2:05 PM joual.f...@gmail.com <joual.f...@gmail.com> wrote:

Hello, I'm trying to convert lidar files originally from EPSG 2950 (MTM CSRS-08) with vertical datum CGVD28 to a new file with a vertical datum CGVD2013. I want to install the grid to transform the file in Z value. It seems I need a .gtx file. How, or where should I get the .gtx file? Is there a link for Quebec territory transformation .gtx grid file? Or Canadian territory transformation grid? Thanks, Frank.

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[brent.m...@gmail.com]

If you have a recent version of GDAL, you should be able to do the vertical datum transformation using gdalwarp. Here's an example:

gdalwarp --debug -overwrite ^
input_cgvd28_rast.tif ^
output_cgvd2013_rast.tif ^
-s_srs EPSG:2950+5713 ^
-t_srs EPSG:2950+6647

Modify the source (s_srs) and target (t_srs) EPSG codes as needed.

[joual.f...@gmail.com]

thanks!