Improvements to the art of orientation measurement are disclosed whereby the phase angle of each of the plurality of orientation dependent radiation patterns is measured at a single common and unique point of measurement on the observation surface and correspondingly in the image of the observation surface, and whereby a central landmark is located at the point of measurement without loss of accuracy in the determination of the plurality of phase angles of orientation dependent radiation so that the precise point of measurement can be determined in the image without errors introduced by an offset between the positions of landmarks and the position of phase angle measurement. Additionally, the preferred embodiment provides characteristics of the central landmark and other landmarks of the orientation dependent radiation source which provide a means to resolve the cosine ambiguity, which is known to those skilled in the arts of image-based orientation measurement as a challenge and source of error for prior-art image-based orientation measurement means.