[gdal-dev] Support for Terrain-RGB

[Rahkonen Jukka]

Hi Javier,

For me VRT with pixel functions  https://gdal.org/en/stable/drivers/raster/vrt.html#derived-bands-pixel-functions feels somehow natural. Now just waiting for someone to show a working example.

Reading the RGB encoded values back to meaningful values would require also metadata about the applied formula if people are willing to use several different/arbitrary  encoding schemas.

-Jukka Rahkonen-

________________________________________
Lähettäjä: gdal-dev <gdal-dev-bounces at lists.osgeo.org> käyttäjän Javier Jimenez Shaw via gdal-dev <gdal-dev at lists.osgeo.org> puolesta
Lähetetty: Torstai 8. tammikuuta 2026 12.20
Vastaanottaja: Lars Ahlzen <lars at ahlzen.com>
Kopio: gdal-dev <gdal-dev at lists.osgeo.org>
Aihe: Re: [gdal-dev] Support for Terrain-RGB

HiIndependently of the convenience of making a new driver or adding it to gdaldem, I am curious about the initial question:Perhaps the same thing could also be achieved using the 
raster calculator (gdal_calc), but that seems far from trivial for most 
users.Is it easy to use a formula to read it? Via a virtual file? Or the new CLI commands?Thanks.On Thu, 8 Jan 2026 at 11:05, Lars Ahlzen via gdal-dev <gdal-dev at lists.osgeo.org> wrote:Good points.Given these and other comments, it sounds to me like we should support different RGB raster formats, as the storage format really is independent from the encoding. Also, supporting Mapbox Terrain RGB, Terrarium RGB, and custom encodings would be desirable. I believe these are all variants of the same thing anyway, with a base (offset) and a scale for each of the R, G and B channels.Even, you probably know GDAL internals quite well, what are your thoughts? If we were to support arbitrary RGB raster formats, would an implementation elsewhere (like gdaldem) be more suitable than a new raster driver, or could a raster driver support different actual file formats?If the latter, could the existing MBTiles driver be used for direct DEM -> RGB tiles (.png/.webp/...) -> .mbtiles generation?- LarsOn 06/01/2026 08:40, Andrey VI wrote: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 <gdal-dev at lists.osgeo.org>:  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'sencoding just enough data to do good enough real-time visualization ofelevation, like hillshading or hypsometric tints, client side.Looks like at least rio-rgbify [1] allows setting a custom base valueand interval. That might be something we want to emulate as well,perhaps as creation options (if a raster format driver) or command lineoptions (if part of gdaldem).- Lars[1] https://github.com/mapbox/rio-rgbify_______________________________________________gdal-dev mailing listgdal-dev at lists.osgeo.orghttps://lists.osgeo.org/mailman/listinfo/gdal-dev--Andrey_______________________________________________gdal-dev mailing listgdal-dev at lists.osgeo.orghttps://lists.osgeo.org/mailman/listinfo/gdal-dev