How is defined the Freak descriptor pattern

Question

I'm have to code my own implementation of FREAK descriptor for a homework. I actually read the original paper but there isn't any explanation of how the build the pattern used.

In the OpenCV code is defined the buildPattern() function but it also lack of documentation on how the pattern itself is build.

So my question is, does anybody knows how the pattern is defined and how the parameters (radius, sigmas and coordinates) are selected?

Answer 1

It looks like the exact values aren't important, but Figure 4 shows the rough layout of the 43 receptive fields.

Their exact geometry is defined by the code here: https://github.com/kikohs/freak/blob/master/src/freak.cpp#L212