r.surf.contour

[Mark S. Gregory]

> I wonder if anyone else is frustrated with this program.
> I am running 4.0 on a Sun.  FOr a moderate sized cell map
> (about 500x500) it is taking 10+ hours to run.  And then
> it is interpolating in a very un-smooth way, *sometimes*.
> ie for some levels it just "steps" down the contour, other times
> it makes nice ramps across them.
> 
> Any comments?
> 
> Simon Cox
> 
As I recall, this program is VERY sensitve to the number and 
distribution of cells with elevation values in the input raster
file.  I believe the manual says that "the programs running time
will increase exponentially with the distance between the contours".

If you have enough (and I do not know how much is 'enough') memory,
use the -f option with r.surf.contour.

My other suggestion is to possibly use r.surf.idw instead.  While 
r.surf.idw is also sensitive to the distance between the raster cells
(generated from the contour lines), r.surf.idw allows for the 
inclusion of 'spot' elevation values (such as converted from sites)
in order to fill in large open areas between contour lines.

The interpolation procedures between these two programs is different,
so I suggest you check the manual to determine the 'best' program for
your needs.  Then there is always s.surf.tps?

Mark Gregory                mg at adasn4.agr.okstate.edu
Oklahoma State University   (405) 744-6417
Stillwater, OK 74078

In one case, we originally converted some vector contour lines into
raster values and then ran r.surf.contour