Rotate a HEALPix map to a new reference frame in pixel space
It is generally better to rotate in spherical harmonics space, see the rotate_map_alms method. A case where pixel space rotation is better is for heavily masked maps where the spherical harmonics transform is not well defined. This function first rotates the pixels centers of the new reference frame to the original reference frame, then uses hp.get_interp_val to interpolate bilinearly the pixel values, finally fixes Q and U polarization by the modification to the psi angle caused by the Rotator using Rotator.angle_ref. Due to interpolation, this function generally suppresses the signal at high angular scales.
Input map, 1 map is considered I, 2 maps:[Q,U], 3 maps:[I,Q,U]
Map in the new reference frame