Related ticket (regarding Terrarium) in
https://github.com/OSGeo/gdal/issues/14520 . I'm not sure what the
solution is, but that proliferation of RGB formats to encode elevations
doesn't look pretty....
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
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