aspect and drainage direction maps
xavi at cataw.uab.es
Thu Nov 23 07:00:00 EST 1995
Many thanks to Philip Verhagen, who answered my question about aspect
and drainage maps generation algorithms. After his help I could arrive to
The aspect map generated by r.slope.aspect seems to be calculated
using the Horn method (as it says the manual), but the results I got
when I made the calculations by hand don't were exactly the same as the
ones I got using the Grass4.1.3 version of this module. At least, if I'm aplyin
by hand the Horn method in a right way.I am following this method such as
it is explained by Shapiro and Westerwelt in r.mapcalc algebra document.
I think the drainage map generated by r.watershed gives the direction
to the lowest neighbour cell, unless there is a pit. In this case it works in
a little different manner, so that it avoids the formation of false pits in the
drainage network. Care must be taken with the region settings to allow
it to work well.
The drainage direction maps generation by r.direct works in
a way I don't understand. It seems clear that it doesn't avoid pits, and that
the algorithm doesn't depend on the way the results will be expressed
(answers, agnps or grass4.0). Does anybody know anything about the
way r.direct generates its maps?
Unitat de Geodinamica Externa i d'Hidrogeologia
Universitat Autonoma de Barcelona
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