That’s the trap @John_Geodesy and myself fell into. It is just a simple “how is the local surface angled to the light source” without any interaction with surrounding surfaces. And for that it yields pretty convincing results.
The way to go is either
-
raytracing if you want physically correct shadows. You can use Blender for example (see my experimentation as posted before, also @Joaquim did some nice work and posted an beginner friendly tutorial for Julia which can be easily adapted to pure GMT)
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texture shading after Leland Brown - currently only available in the Julia Wrapper but it has potential for highlighting terrain features without dropping the “shadow” side into pitch black darkness. You don’t get correct shadows but you get nice depth and border information which can be combined with some traditional hill shading for some nice plots. Maybe this is something for @John_Geodesy as well.
See the threat over on GitHub for some more examples.