[gdal-dev] Support for Terrain-RGB

[Lars Ahlzen]

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