I have a DEM raster. I have a polygon representing a hole.
How do I combine the two, so that I have a new DEM whose elevation, in the area bounded by the polygon, has been adjusted according to whatever height value I assign the polygon?
Things I've tried:
- Rasterizing the polygon and combining it with the existing DEM, which gets me a hole, but requires an insanely high resolution on the DEM or else I get jagged edges.
- Giving an extrusion of the polygon a negative value, so that when rendered in 3D I get a hole. Unfortunately, the render still projects both the DEM and the polygon separately, so the "hole" is covered by the DEM. I still need to cut a hole in the DEM to reveal the polygon below.
- After the last bullet point, I vectorized the DEM, cut a hole in it that matched my hole-polygon, and then extruded it -- and realized that in the 3D view, the extrusion is invisible if the camera angle is in the wrong plane. e.g. if my camera angle is looking at the ground from above, the extruded polygon with a negative value is invisible. If I pan the camera "under" the ground plane, so I'm looking back up at the ground from underneath, the extruded shape is visible, but everything else is invisible. I also have the problem of having the top face of my polygon, the one level with the surrounding DEM, effectively blocking the opening to my hole.
I ultimately want to be able to model a hypothetical hole and assign z-axis values to particular point data located within the ditch.