I use Digital elevation models quite a bit in my work for realistic topography.
I haven’t had a problem with downloaded free topo from governments or BlenderGIS, however this last one I am working with is causing me issues in that displacement textures or BlenderGIS surface imports just dont work.
Best I can tell in my trouble shoot is that the pixel sizes are so small… normally I deal in 1 or 25 pixel size… is this something that is a flag? What is an ideal pixel size? or other things I should check on the raw Tiff?