Hi all.
It would be great to have RGB DEM support in GDAL.
Some considerations.
1. It makes sense to add support not only for Mapbox Terrain RGB, but also for
Mapzen Terrarium RGB [1][2] encoding. Mapbox and Maplibre support both
encodings, the latter also supports custom encoding [3][4]. Therefore, support
for custom encoding will also be useful.
2. I don't quite understand why only PNG format is being discussed here. It is
possible to encode a DEM into any raster RGB image format. Moreover, PNG isn't
the most optimal of them [5]. In my opinion, the WEBP format is preferable. For
example, Maptiler uses it for Terrain RGB and Ocean RGB datasets [6].
3. Ideally, the output should be not just an encoded image, but tiles ready for
use in Mapbox/Maplibre/etc., including in the form of data sets (MBTiles,
PMTiles).
[1] https://www.mapzen.com/blog/terrain-tile-service/
[2] https://github.com/tilezen/joerd/blob/master/docs/formats.md#terrarium
[3] https://docs.mapbox.com/style-spec/reference/sources/#raster-dem-encoding
[4] https://maplibre.org/maplibre-style-spec/sources/#encoding_1
[5]
https://medium.com/@frederic.rodrigo/optimization-of-rgb-dem-tiles-for-dynamic-hill-shading-with-mapbox-gl-or-maplibre-gl-55bef8eb3d86
[6] https://www.maptiler.com/on-prem-datasets/dataset/terrain-rgb/
>Tuesday, January 6, 2026 0:46 AM +03:00 from Lars Ahlzen via gdal-dev <
>[email protected] >:
>
>On 05/01/2026 19:47, rayg wrote:
>> Strange encoding, -10000 meters isn't deep enough for the Marianas
>> Trench. You could borrow another 10 km from the 1.6 million meters
>> still available on the positive side.
>>
>> Scaling by 0.1 also means a 10 cm vertical resolution., which is
>> useless for some use cases. The 24 bits per pixel could be much better
>> allocated.
>
>I kind of agree with both points, but I guess the format is what it is.
>
>I don't think it's supposed to be a general-purpose storage format. It's
>encoding just enough data to do good enough real-time visualization of
>elevation, like hillshading or hypsometric tints, client side.
>
>Looks like at least rio-rgbify [1] allows setting a custom base value
>and interval. That might be something we want to emulate as well,
>perhaps as creation options (if a raster format driver) or command line
>options (if part of gdaldem).
>
>- Lars
>
>[1] https://github.com/mapbox/rio-rgbify
>
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--
Andrey
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