On Jul 9, 2007, at 3:47 PM, Dylan Beaudette wrote:
On Wednesday 04 July 2007 08:41, Glynn Clements wrote:
"Carlos \"Guâno\" Grohmann" wrote:
Interesting.
Why r.slope.aspect uses
dx = ... / (4 * ewres);
while r.shaded.relief uses
dx = ... / (8 * ewres);
??
Oops. It should be 8; the ewres/nsres values are actually the
distances between the centres of the top/bottom rows and left/right
columns in the 3x3 window, which are two rows/columns apart. IOW, the
4*ewres should have been 4*(2*ewres) = 8*ewres, ditto for nsres.
Yikes, does this mean that previous calculations are now wrong?
no - it is correctly implemented - you would have found that it is
wrong by now.
It is just that the variable that you divide with in the r.slope.aspect
uses 2*ewres (twice the resolution, not just one as is usual in
the published equations) - I got caught on that many times when checking
the r.slope.aspect code.
Helena
dylan
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