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GlacioHack / xdem

Analysis of digital elevation models (DEMs)
https://xdem.readthedocs.io/
Apache License 2.0
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Update reference for curvature #577

Open adehecq opened 3 months ago

adehecq commented 3 months ago

At this line, the doc says that the reference for the curvature is Zevenbergen and Thorne (1987). However, equation 16 in this ref is different from the implementation in xdem at this line (-2(D + E)). This equation is instead used in Moore et al. (1991) (equation 16).

Also I noticed a mistake in the description of the curvature. "convex (like a mountain peak)" and "concave (like a through or a valley bottom)" are wrong and should be "concave (like a mountain peak)" and "convex (like a through or a valley bottom)". But one needs to check which one corresponds to negative/positive curvature.

rhugonnet commented 2 months ago

Good catch. This means RichDEM is also wrong on that formulation, as we test against it and it cites Z&T: https://github.com/GlacioHack/xdem/blob/34e5049ae76a858b9c95c8763d9763b298c56e3c/tests/test_terrain.py#L208

Should we then implement both the formulations of Zevenberg and Thorne and of Moore et al.? It would be weird to have all curvatures based on Z&T except the one.