[gdal-dev] Support for Terrain-RGB

[Lars Ahlzen]

Hi Even,

On 05/01/2026 14:50, Even Rouault wrote:
> I would rather see that as a standalone TerrainRGB raster driver, 
> leveraging the PNG driver underneath.

That was my original thought as well. Then, after thinking about 
different use cases I thought adding a gdaldem mode would allow for a 
wider range of workflows.

That said, you probably have a better idea of what would work best for 
GDAL as a whole, so I can look in that direction.

> 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") ) 

I don't think there's any sort of indication of the encoding in the 
files themselves (please correct me if I'm wrong). I imagine the need to 
decode Terrain-RGB back into a single-band DEM would be rare anyway, so 
a write-only driver might be sufficient.

- Lars