Differential Invariants on the depth Image (documentation in-process/unfinished)

One of the most appealing things to me about the kinect is that we can use the full arsenal of differential geometry to analyze and extract features from the detected surface.

For example, the gradient gives us the normal of the surface at point (x,y,z).

An example of finding the surface normals on the image of Lena , can be seen below. Something that needs to be noted is that the intensity values of this 2d image are treated as elevation values.
Code at: github