Q: s.surf.idw

GRASS GRASS user
1

We do have a site-list of field measurements
(soil resistivity) which we interpolate to
raster by means of s.surf.idw.

Z-values in the site-list are floating-point
ranging from 0.0 to 25.0.

The output of s.surf.idw creates a raster map with
only five categories.

I need at least 255 categories, how can this be
accomplished ?

Do I have to build categories outside grass, i.e.
create the site-list with categories for Z-values
instead of using original (measured) data ??

Thanks for your help,

Andreas
Dept. of Geophysics
Univ. of Bremen

2

On Fri, 22 Nov 1996, A. Rosenberger wrote:

We do have a site-list of field measurements
(soil resistivity) which we interpolate to
raster by means of s.surf.idw.

Z-values in the site-list are floating-point
ranging from 0.0 to 25.0.

The output of s.surf.idw creates a raster map with
only five categories.

I need at least 255 categories, how can this be
accomplished ?

Do I have to build categories outside grass, i.e.
create the site-list with categories for Z-values
instead of using original (measured) data ??

Thanks for your help,

Andreas
Dept. of Geophysics
Univ. of Bremen

Adreas,
Multiply your Z values by 10 (use awk). Now you know why the next phase
of GRASS was going to be floating point! Regards,
--
Malcolm D. Williamson - GIS Specialist E-mail: malcolm@cast.uark.edu
Center for Advanced Spatial Technologies Telephone: (501) 575-6159
Ozark Rm. 12 Fax: (501) 575-5218
University of Arkansas
Fayetteville, AR 72701

3

In article <9611221338.AA11278@gphsun1.uni-bremen.de>,
andreas@gphsrv1.geophyS2.uni-bremen.de says...

We do have a site-list of field measurements
(soil resistivity) which we interpolate to
raster by means of s.surf.idw.

Z-values in the site-list are floating-point
ranging from 0.0 to 25.0.

[ ... ]

Thanks for your help,

Andreas
Dept. of Geophysics
Univ. of Bremen

Andreas, I would try multiplying your Z values (resistivity)
by some scalar (say 10), and trying again. You may be
getting bitten by the fact that most (some?) of GRASS is
integer.

Gordon Haverland
Precision Farming Project
Alberta Agriculture