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Hill shading

Friday 21 September
by ggjj
in forum
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On most topographic maps*, the shade used to reinforce relief assumes a light source at the North West (OpenCycleMap and OpenTopoMap are examples). Reality is otherwise, but this somehow is natural to the brain, and it gives a good impression of the actual landscape.

On however, the shade seems to only depend on the norm of the elevation gradient, i.e. the steepness of the slope. This results in pictures such as the one below, where valleys and ridges are hard to distinguish on first sight.

Would it be possible to modify the shading formula so that it gives better/more standard results?

*at least in the northern hemisphere.


Sat 22 Sep 2018, 15:56

Coincidentally I'm experimenting with this at the moment – the new version of the program that does the hillshading (GDAL) has some interesting new options. Watch this space!

Sat 22 Sep 2018, 20:56

Oh, that's great, I'm looking forward to it!

Mon 24 Sep 2018, 15:42

I’ve just made a new version of the hill-shading live for Europe (not America yet). It uses the new ‘multidirectional’ shading in GDAL which gives a really good view of the lie of the land. There’s still a few tweaks I’d like to make but I think it’s looking better!

You’ll probably need to do a shift-refresh for the new tiles to come in.

Mon 24 Sep 2018, 15:43

(Here’s an example where I’ve been testing it: Winchcombe, Gloucestershire, UK)

Tue 25 Sep 2018, 17:36

It's looking better like this, bravo!

One suggestion: the darkest shade should be a bit lighter, as it is now the contrast in mountains can be too high (in my opinion). See around Saint-Christophe en Oisans (FR) [1] and compare with OpenCycleMap [2]. In any case, it's much easier to read the map now.