[GRASS-user] v.extrude: advice on generating 3D building

[cheg01 at comcast.net]

I am trying to use v.extrude to generate buildings of varying height. I have a vector file with all of the building outlines and I have a raster file that contains high resolution height data extracted from LIDAR files.  I don't understand the function of v.extrude. I tried specifying the raster file name in the "elevation=" option but I get an error that says I have to either use a constant height in "height=" or specify an attribute table column with height data in "hcolumn=".  What does the "elevation" option do? Any suggestions on easy ways to populate a height data column from a raster file?