Re: [GRASS-user] slope calculation under lat long
Thanks Moritz, my understanding on this is that a pixel with delta elevation of 100m will create different slope values due to the change of the Pixel dimension going from the equator to the north location. This observation is valid for the east-west slope because of the distance change in the x dimension, rather for the north-south slope the y dimension stays constant and so the slope remains the same. In other words, is there any other correction that will take this in to account? Thank you Giuseppe On Thu, 19 Mar 2020 at 12:06, Moritz Lennert wrote: > On 19/03/20 16:37, Giuseppe Amatulli wrote: > > Hi, > > I wondering if the slope calculation in GRASS > > (https://grass.osgeo.org/grass78/manuals/r.slope.aspect.html) take in > to > > account the > > latitudinal change of the meridian distance or just simply treats the > > raster as square grids also under lat long system (WGS84)? > > AFAIK, r.slope.aspect uses the G_distance() function which calculates > geodetic distance if in a Lat-Long location, so yes it takes into > account latitudinal change. > > If it doesn't, I would consider this a bug. > > Moritz > -- Giuseppe Amatulli, Ph.D. Research scientist at School of Forestry & Environmental Studies Center for Research Computing Yale University New Haven, CT, USA 06511 Teaching: http://spatial-ecology.net Work: https://environment.yale.edu/profile/giuseppe-amatulli/ ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] slope calculation under lat long
On 19/03/20 16:37, Giuseppe Amatulli wrote: Hi, I wondering if the slope calculation in GRASS (https://grass.osgeo.org/grass78/manuals/r.slope.aspect.html) take in to account the latitudinal change of the meridian distance or just simply treats the raster as square grids also under lat long system (WGS84)? AFAIK, r.slope.aspect uses the G_distance() function which calculates geodetic distance if in a Lat-Long location, so yes it takes into account latitudinal change. If it doesn't, I would consider this a bug. Moritz ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] slope calculation under lat long
Hi, I wondering if the slope calculation in GRASS (https://grass.osgeo.org/grass78/manuals/r.slope.aspect.html) take in to account the latitudinal change of the meridian distance or just simply treats the raster as square grids also under lat long system (WGS84)? In case of "treats the WGS84 raster as square grids" the only solution to obtain better results is to resampling the DEM to UTM or to Equi7. Thank you Giuseppe -- Giuseppe Amatulli, Ph.D. Research scientist at School of Forestry & Environmental Studies Center for Research Computing Yale University New Haven, CT, USA 06511 Teaching: http://spatial-ecology.net Work: https://environment.yale.edu/profile/giuseppe-amatulli/ ___ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
