[GRASS-user] slope calculation under lat long

Giuseppe Amatulli giuseppe.amatulli at gmail.com
Fri Mar 20 08:24:18 PDT 2020

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
Thank you

On Thu, 19 Mar 2020 at 12:06, Moritz Lennert <mlennert at club.worldonline.be>

> 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
Teaching: http://spatial-ecology.net
Work:  https://environment.yale.edu/profile/giuseppe-amatulli/
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