[GRASSLIST:10552] TOPIDX flow direction algorithm

[twiens]

I'm working with some ArcGIS users and in a note in the AML
script to calculate the topographic index, the author notes
that ArcInfo uses a D8 algorithm to calculate the
contributing area. The concern is that for relatively flat
areas, the index value will be inaccurate or inappropriate.
I've noted in areas that I have generated a topographic
index, that flat areas seem to be set to NULL by topidx.

I've not been able to find any reference to this issue in
the topidx documentation. Can someone tell me if this
concern is valid for r.topidx?

Thanks

T
--
Trevor Wiens
twiens at interbaun.com