GradientMaps orientation is wrong (This affects HOG descriptors)

Created by: laurentes

There is a bug when computing the orientation maps using the bob::ip::GradientMaps class. This currently affects the computation of HOG descriptors.

This was originally caused by a mistake in the blitz++ documentation available at late www.oonumerics.org. A copy of this documentation can be found here, with the mistake: http://www-cecpv.u-strasbg.fr/Documentations/blitz/blitz_3.html#SEC89. The signature of the blitz::atan2 reduction is indeed wrong. The correct version is blitz::atan2(y,x) instead of the blitz::atan2(x,y). The fixed version is consistent with the signature of the standard function atan2(y,x) (http://www.cplusplus.com/reference/std/valarray/atan2/).