# Call for help!

Mitch Rauth rauth at tyche.tyche.mat.univie.ac.at
Tue Jan 3 12:34:30 EST 1995

```Hallo everybody!

I am a mathematician from Vienna, working on the field of scattered data=20
approximation. For the application of some methods from geostatistics=20
(external drift kriging) to real world data from hydrology, I have to=20
incooperate information from a digital elevation model, and found GRASS=20
in our computer network which might be just the right tool for me.

As I am a complete beginner in this field, I would really appreciate=20
all help or hints to the following problem:

I=ADve got the elevation model as xyz-data on a grid of 50m, and for each=
=20
point I would like to determine the following  two quantities:

1)  The area which drains into this point, i.e. all points uphill from=20
which water can flow down to the point under consideration, and

2) The angle between the surface and the horizontal plane. I think this=20
is called the slope or so.

The motivation for this is the following idea: I am trying to estimate=20
the moisture of the soil, and thought that it might be related to the=20
topography. The bigger the area from which a point recieves water the=20
wetter the soil. On the other hand, if the slope is very steep, then=20
the water will accumulate somewhere downhill, decreasing the water content=
=20
of the ground.

Maybe the two questions are completely trivial, but I would really find any=
=20

Thanks  a lot,
=09=09Mitch Rauth

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Michael Rauth                                   e-mail:
University of Vienna                            rauth at tyche.mat.univie.ac=
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A-1090 VIENNA                                   phone: ++43-1-4088311/4
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```