Surface with r.surf.contour??????

[G. Zacharioudakis]

Here is another problem I got.

In the manual it is mentioned about r.surf.contour that two 
of the conditions for using it are:
1) Contour lines extend to the edge of the current region.
2) No disjoint contour lines.

I have a contour map representing the elevation of the top of 
boulder clay in my area, containing only 4 lines 10,20,30,40 mtrs.
The values decrease from 40 at the NW  to 10 at the SE.
At the north and west of  the area, the contours are extended to the edge 
of the region. This does not happen at South and at east. I changed the south e
dge 
of  the region and the countours were extended up to the south edge as well.
But there is a lot of space between the last line SE and the east edge. So usin
g 
r.surf.contour I got wrong data to this area and allthough I had to take values
 less 
that 10 (which is the last contour towards SE) GRASS gave me gradually bigger.

If I mask the region using as mask the area that is enclosed by the 
10 m  contour(which surrounds the rest of contours)  then  things will be bette
r?
If I wanted to have a guess for where the 0 m surface is (without having the re
lative contour)
is there  a way to do it?
These alterations will affect future use of  r.mapcalc in relation with raster 
data
 from the whole region (in terms of visual output mainly).

Thanks once more.
Giorgos
 
Giorgos Zacharioudakis
School of Earth Sciences 
University of Birmingham
Edgbaston B15 2TT
Birmingham
UK
Tel 0044 121 4146146
Fax 0044 121 4143971
e-mail:giorgos at ers.bham.ac.uk