[GRASS-user] What output from r.topidx?

[Rich Shepard]

On Thu, 11 Feb 2010, Markus Neteler wrote:

> here please run
> r.univar house_elev
> to check for the map statistics.

Markus,

   I have a map from running r.terraflow and had the masked map from
r.water.outlet, so I didn't need to run r.topidx. I also didn't need to run
the r.mapcalc command on the bottom of the man page as I already have that
mask.

   Anyway, recognizing that the topographic index is dimensionless and
probably sensitive to unmeasured variables in my project area, is there
anything I can infer from the map and the statistics?

   The results of r.univar are:

total null and non-null cells: 110694756
total null cells: 148468

Of the non-null cells:
----------------------
n: 110546288
minimum: 0.381453
maximum: 20.1172
range: 19.7357
mean: 4.82972
mean of absolute values: 4.82972
standard deviation: 1.89492
variance: 3.59074
variation coefficient: 39.2347 %
sum: 533907122.1373398304

and a jpeg image of the area of interest is attached. Specifically, the area
around the uppermost triangle is important. I see that the TCI values are
high along the stream channel leading there and low to the north, west, and
south. Can I say anything intelligent about the wetness index around that
triangle based only on this map?

Thanks,

Rich