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?
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?
On Friday 24 February 2006 07:31 am, 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@interbaun.com
I would highly recommend enabling c++ support when you compile GRASS, so that
you have access to the r.terraflow . This will compute a TCI, and in many
cases I have found the output from r.terraflow to be superior to the
analogous commands in GRASS.
cheers,
--
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341