[GRASSLIST:10556] Re: TOPIDX flow direction algorithm

Huidae Cho grass4u at gmail.com
Fri Feb 24 12:32:19 EST 2006

r.topidx has the same issue that flat areas have NULL topidx values since
contributing areas cannot be calculated with the D8 algorithm when area is
float.  Is there any way to work around this flaw or is this really a bug or a
feature of the algorithm?

Huidae Cho

On Fri, Feb 24, 2006 at 08:31:19AM -0700, twiens wrote:
> 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

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