[GRASS-user] Curvature in r.slope.aspect

[Glynn Clements]

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 at gclements.plus.com>