[GRASSLIST:5318] v.surf.rst and "gully"

[Ivan Marchesini]

Hi to all
I tried to use v.surf.rst!!!
I have to create a higth resolution DEM (1 m raster cells) of the landscape 
along a river....
the problem is that this river has an oblique path on the screen, from NO to 
SE....
So, setting the region of the study area to match the river path, I 
interpolate a lot of landscape I don't need.... with obvious problem of time 
to obtain the results...
because I have georeferenced aerial photos of the river I tried to use the 
mask option of v.surf.rst, setting the mask to match a single photo, but I 
didn't obtain good results... and the same using the MASK option of grass....

I also tried to use the procedure explained in the book Open Source 
Gis.........(Neteler-Mitasova) about the generation of a dem in a surface 
with faults (gully.mask, etc......). 
but I didn't understand why they use an inverse mask to obtain only the DEM of 
the gully..... 

They have a gully area named "gully.mask" and a lot of points of the gully 
topografy "gully.ascii"

They transform the ascii file in site grass data:

s.in.ascii elev.gully input=gully.ascii

after, they obtain the inverted mask:

r.mapcalc gully.mask.inv = "if(gully.mask,0,1)"

then, they use s.surf.rst:

s.surf.rst elev.gully elev=elev.gully mask=gully.mask.inv

They say that in this way is possible to interpolate only in the area of the 
gully and not in the hillslope around....

The problem is:
the raster gully.mask.inv is a map that have value 0 inside the area of the 
gully and 1 outside....
so, I think that, using the antecedent sintax, I obtain an opposite result 
!!!!!!

Can someone help me??

Thank you and sorry for the lenght of the e-mail.....

Ivan











can someone help me????