In true stackexchange tradition. I am interested to see how people approach generating a good quality displacement map from existing 3D geometry. For completeness, list the qualities that make up a good displacement map. I'm not looking for links to external tutorials, but short descriptions of your methods are welcome.
My current method involves setting up a orthographic camera viewing the geometry, and setting the far and near clipping field to the extents of the geometry. Then render the image and extract the z-buffer by normalizing it so it becomes a grey scale and outputting that as a file from the compositor.
I will elaborate on my method as an answer, if no one offers a more convenient procedure.