[gdal-dev] Using GMT CPT file with gdal raster color

[Even Rouault]

Sean,

thanks for the report. Support for GMT .cpt files dates back to 2010 and 
hasn't evolved much since. So I assume GMT .cpt format might have 
changed a bit since then. I've submitted a fix in 
https://github.com/OSGeo/gdal/pull/14595 to support new files. In the 
mean time you can manually adjust your .cpt file to please current 
released GDAL versions by:

- replacing slashed with space

- and removing the trailing " L"

Even

Le 17/05/2026 à 22:24, Sean King via gdal-dev a écrit :
> Hi folks,
>
> I'm using GMT version 6.6.0 and GDAL version 3.12.4. I have 
> several CPT files that I generated in GMT using the makecpt command, 
> such as:
>
> */gmt makecpt -T-120/120/10 -I -Crainbow -Z -Fr/*
>
> which generates the attached file. Then, I am trying to apply that 
> color palette to a TIFF file using 'gdal raster color'. The 
> documentation <https://gdal.org/en/stable/programs/gdaldem.html> 
> states that
>
> */GMT .cpt palette files are also supported (COLOR_MODEL = RGB only)./*
>
> however, I continually get the error of
>
> */ERROR 1: No color association found in test.cpt/*
> */
> /*
> When I dug into the GDAL source code for the GMT CPT parser here 
> <https://github.com/OSGeo/gdal/blob/b3f839f2515b023e4a7cf099b7ce1626ccb24eac/gcore/gdalcolortable.cpp#L744>, 
> it really does not seem to match up with the current implementation of 
> GMT CPT files, even though the GDAL feature was added in the latest 
> release. For instance, it uses space, comma, tab, and colon as 
> delimiters, but no matter what flags I use for my GMT CPT generation, 
> I get a backslash as the delimiter, as seen in the attached file. 
> There are other inconsistencies as well.
>
> Am I missing something? I'm somewhat new to GDAL and GMT, so I'd 
> appreciate any advice. Also, if this feature really to read GMT CPT 
> files is not adequate, is there a better way to approach this? I 
> essentially want to colorize a .grd file using gdal, so that I can 
> then generate map tiles with it. I have the rest of the pipeline 
> figured out, but I'm having issues with the color mapping. I wrote my 
> own converter from GMT CPT to GDAL color file, but it's a bit 
> buggy/hacky. I'm wondering if there is a more 'official' way to do this.
>
> Thanks!
> Sean
>
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