[GRASS-user] 3D Buildings

[cheg01 at comcast.net]

I am trying to generate a model very much like the screenshot of Trento on the Grass home page using data for the city of Seattle. I have building outlines and heights in a vector map and accurate elevation data in a raster file. I have used v.extrude to construct the buildings. When I try to plot them in nviz, I get odd disjointed floating surfaces rather than the solid looking 3D objects objects in the Trento example. The extruded vector coverage has only faces, no lines, areas, or centroids. Is that normal? I tried extruding both with and without the "trace" flag set. 

What commands were used to create the beautiful model of Trento? Was it something other than v.extrude and nviz?