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osmandapp / OsmAnd

OsmAnd
https://osmand.net
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Slope color map does not represent true slope of terrain #20797

Closed marcelharing closed 4 weeks ago

marcelharing commented 1 month ago

Description

My gut feeling was that the slope map based on OsmAnds DTM underestimated the steepness of the terrain (which would not be good for avalanche risk assessment), so I compared it with Sonnys 50m DTM and openslopemap.org low resolution layer (20-30m) in QGIS with the avalanche color ramp from OsmAnd:

Although Sonnys DTM resolution is lower, it represents the terrain much better. OsmAnd's DTM somehow underestimates it? I don't know why, but maybe you smoothed it too much? Afaik you also use Sonnys DTMs, but the 50m or the 20m resolution DTMs?

Steps to reproduce

Calculate the slope of OsmAnd's DTM and Sonnys 50m DTM (in this case for Austria) and style it based on the predefined avalanche color map of OsmAnd with slope steps of 30°, 35°, 40°, 45° in QGIS or add OpenSlopeMapLayer LR TMS Layer.

Actual result

Slope steepness underestimated

Expected result

See picture for comparison

Your Environment (required)

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OsmAnd Version: 4.8
Android version: 13
vshcherb commented 1 month ago

In OsmAnd you can use different geotif (though it should be in Mercator projection), and it could be much more detailed. Mostly artifacts are related that maps are condensed and don't have enough details for slope maps. As I remeber OsmAnd maps are roughly 50m per pixel in many regions.

xmd5a2 commented 4 weeks ago

See https://github.com/osmandapp/OsmAnd/issues/6636

xmd5a2 commented 4 weeks ago

This happens cause in app we use height maps with lower resolution than sources we used to obtain these data. But I've changed avalanche color palette a bit and now it reflects slope much better in my opinion. Image

DmitryAlexei commented 1 week ago

Later (bottom right corner)

Today

OsmAnd~ 4.9.0#3365m, released: 2024-10-07 Color scheme > Avalanche, transparency 100% go to coordinates 47.21036 11.54391 and see, that The Avalanche scheme now much more convenient for avalanche risk assessment.