[GRASSLIST:7949] how do I make a 3D mask for v.vol.rst?

[Eva L. Hulse]

I'm interpolating volumes that represent concentrations of chemical 
components in soil.  Ideally, the volumes wouldn't extend above the 
surface of the ground.  Right now, the interpolated volumes are 
extending all the way to the uppermost z-value in my region, regardless 
of where the ground surface is.  This could have something to do with 
the z-values being offset (as mentioned in Benjamin Ducke's email), but 
since the top of my region =1, and the uppermost z-value for my data is 
0.23, i still feel like the volumes shouldn't go all the way to z=1.

I understand the mask in v.vol.rst just masks out horizontal areas based 
on a 2D raster (i could be wrong).  Can i mask out vertical areas?  Or 
am i doing something else weird?

v.vol.rst input=kknPVect0816 wcolumn=w tension=40 smooth=0 segmax=700 
dmin=0.1 npmin=2 wmult=1.0 zmult=1.0 elev=0817kknPvol

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Eva L. Hulse
PhD Student
University at Buffalo Anthropology Department
evahulse at buffalo.edu