Not optimal gdaldem "scale-factor": the projection is already know (and possibly coordinate dependent)

[cate]

Hello,

I find the scale factor in gdaldem (e.g. hillshade and slope) not very useful. The geoTiff already know the projection and so the horizontal and vertical units. The factor -z could be used to fine-tuning the projections of shading.

Additionally such factor could be coordinate dependent (e.g. varying by latitude).

So I propose a new flag -S with force gdal to use geoTiff projections and units (and so, no more scale=111120 factors).

[Jukka Rahkonen]

I believe that most DEM files are using some 2D projection like UTM ​http://epsg-registry.org/export.htm?wkt=urn:ogc:def:crs:EPSG::32635 so vertical units are unknown. If the coordinate system is metric heights are probably metric too and using the same unit as for x and y for z multiplied with "-z" would give a correct result but it is only guessing.

Especially with projections like EPSG:4326, on what basis would you select meters as vertical unit because only Lat and Long axis are defined ​http://epsg-registry.org/export.htm?wkt=urn:ogc:def:crs:EPSG::4326?

If there was an automatic -S switch I would like to have also -s switch for overriding the automatic scale.

[Jukka Rahkonen]

I would say that this can be implemented only after the Z dimension is really handled in GeoTIFFs, compare with #7093.

[Even Rouault]

This ticket has been automatically closed because Trac is no longer used for GDAL bug tracking, since the project has migrated to GitHub. If you believe this ticket is still valid, you may file it to ​https://github.com/OSGeo/gdal/issues if it is not already reported there.