How to develop a dem map

[Antonio Rodríguez Verdugo]

Hi Michael,


>> I'm trying to develop a dem map, but instead of altitudes, I want to
>> display animal and plant population densities. I've tried with v.digit to
>> create a contour map, then v.to.rast, and then r.surf.contour. But I do not
>> get a good result. I think my problem is in the v.digit module, I don't
>> know exactly how to define the lines or areas regarding  densities.
>
>It depends on what you have as initial data : if you have some
>"isolines" for the density, you can digitize them, giving each
>line a density as attribute, then v.to.rast and r.surf.contour.
>Your line contour map should be seen exactly as a altitude contour
>map.  So it is important that each line is labelled with the
>number it represents.

Yes it works. But I didn't know that I needed a lot of contour lines in
order to run fast the r.surf.contour module. With few isolines I get a very
poor performance ( I needed two or three hours), so in the beginnings of my
search I thought I was doing somenthing wrong (I used Ctrl-C in order to
stop those endless processes)  . Maybe is my processor (pentium 166).

>
>If you have mesured the density at some places, you will find
>easier to enter your mesures in a site file (x, y, value), then
>run s.to.vect then v.to rast, and finaly s.surf.tps. You will
>interpolate between points instead of lines.

With s.surf.tps I only get a plain raster file with no appreciable data. I
tried with s.surf.idw, and it seems to fit my needs. But when I run the
d.3d module I get some "holes" or depression as if I put negative values,
but it isn't the case. So I think I must tune up something.

Thanks,

Antonio Rodríguez V.
IRNAS-CSIC
Sevilla, Spain