How can I create polygons for a 3D map from a DEM in grass/qgis

Question

I have a SRTM 30m DEM of my area. I want to create a physical 3D terrain map from it (from felt, 3D printer, you name it). I have two questions about this process:

With grass r.contour I created contour lines from the DEM, and with v.generalize I smoothed the contour lines. Some of those contour lines still have gaps in them though. How can I make those contour lines smoother and interpolate in between so that two isolines that have the same elevation and have a 10m gap between them, are actually connected.

And more importantly, I would like to know how I can make polygons that correspond to the whole surface area with that height, so I can print those polygons (and cut them from felt, or input them in a 3D printer) to create polygons that I can stack on top of each other and create a 3D terrain map. How can I do this? I already have the isolines, the land outline and the bounding box outline for my area. I just need to somehow connect the isolines to the bounding box and land outline to create a polygon, for each isoline.

Any suggestions? I mainly use grass and qgis, but any other FOSS package is fine as well.

Answer 1

Maybe a slightly different approach will match your needs. Try looping thru all the elevations that you will be snipping from felt, and create a raster for each, then convert each to a polygon vector. You'll end up with lots of separate polygons, one for each elevation, ready for the scissors.

For e in 10 20 30 40 50 60 70 80 90 100; do
    r.mapcalc "elev_$e = if(dem <= $e, $e, null())";
    r.to.vect -s -v input=elev_$e output=elev_poly_$e feature=area;
    g.remove -f rast=elev_$e;
done