Hi,
I use a z factor in slope and hill shade calculation when my DEMs are in
Long/Lat and the altitudes in metres (like SRTM, ASTER GDEM...). In
GdalDem , there is not a z factor or a scale option for Aspect (0-360D
azimuth) but in the Qgis terrain analysis, there is. (It does not appear
to work in Qgis 2.18.24).
In Qgis 3.2.3, when using the QGIS Terrain analysis Aspect algorithm
with a z factor of 1, I get identical results as in gdaldem and results
look and feel good. I figure it's probably the same algorithm running
in the background. What more, the aspect file is similar to result
done on a reprojected DEM in a local UTM zone (where no z factor is
needed as everything is in metres). Reprojecting is not an option for
my project.
In the QGIS Terrain analysis Aspect algorithm, if I use 0.0000126 as the
correct z factor for the area (1 / The length of a Degree of Longitude
in metres at a latitude of 45N) (or 1/78847=0.0000126) my results are
very wrong.
I wonder if using a z factor (0.0000126) is not needed for the aspect
calculation and that this should be removed from the QGIS Terrain
Analysis aspect options. Any thoughts?
Nicolas
_______________________________________________
Qgis-user mailing list
[email protected]
List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
