[gdal-dev] Support for Terrain-RGB

[Even Rouault]

Hi Lars,

I would rather see that as a standalone TerrainRGB raster driver, 
leveraging the PNG driver underneath.

For the read side, if one is desired (write-only drivers are possible), 
is there a way in metadata or file naming of distinguishing a regular 
RGB PNG file from a Terrain-RGB one? If not, the Identify() function 
should rely on users providing a "TerrainRGB:" prefix or specifying 
explicitly the driver in the GDALOpenInfo::papszAllowedDrivers member 
(testable with  poOpenInfo->IsSingleAllowedDriver("TerrainRGB") )

Even

Le 05/01/2026 à 15:15, Lars Ahlzen via gdal-dev a écrit :
> Hi all,
>
> For Open/WebGL-based client side map rendering libraries, like 
> MapLibre or Mapbox GL, Terrain-RGB [1] (original spec by MapBox I 
> believe) seems to be the elevation encoding of choice.
>
> The encoding itself, meant for use with 8-bits per channel RGB raster 
> formats such as PNG tiles, is straightforward:
>
>  elevation (in meters) = -10000 + 0.1 * (R * 65536 + G * 256 + B)
>
> As far as I know a separate tool is typically used for the encoding, 
> such as rio-rgbify [2] from Mapbox. There's an example writeup of such 
> workflow at [3]. Perhaps the same thing could also be achieved using 
> the raster calculator (gdal_calc), but that seems far from trivial for 
> most users.
>
> It looks like it would be relatively easy to add native support for 
> this in GDAL, perhaps as another mode in gdaldem. Would it make sense 
> if I gave that a try?
>
> - Lars
>
> [1] https://blog.mapbox.com/global-elevation-data-6689f1d0ba65
> [2] https://github.com/mapbox/rio-rgbify
> [3] https://github.com/syncpoint/terrain-rgb/blob/master/README.md
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/gdal-dev

-- 
http://www.spatialys.com
My software is free, but my time generally not.