GRASSusers,
I have a very simple question regarding the output of r.slope.aspect.
I know that slope and aspect are the first derivatives of elevation and are
expressed in degrees, while profile and tangential curvatures are the second
derivatives of elevation. What I would like to know is the units in which
curvatures are expressed.
In other words, what does it mean a curvature of 0.05?
Thanks in advance.
Aldo Clerici
Parma University
Aldo Clerici wrote:
I have a very simple question regarding the output of r.slope.aspect.
I know that slope and aspect are the first derivatives of elevation and are
expressed in degrees, while profile and tangential curvatures are the second
derivatives of elevation. What I would like to know is the units in which
curvatures are expressed.
In other words, what does it mean a curvature of 0.05?
Curvatures will be in 1/metres, e.g. a curvature of 0.05 corresponds
to a radius of curvature of 20m.
Note that if your elevations aren't in metres, you need to use the
zfactor= option (e.g. zfactor=0.3048 if elevations are in feet).
Also, if your coordinates are in feet, you need to ensure that the
PROJ_UNITS file reflects this, otherwise you will get incorrect
results.
For lat/lon locations, the degrees-to-metres factor will be computed
automatically for each row (close to the poles, where the horizontal
scaling changes rapidly with latitude, I would expect the calculations
to be quite inaccurate).
--
Glynn Clements <glynn@gclements.plus.com>