1. A method of determining a component of a location of a radiation source within a three dimensional volume, the method comprising the steps of: passing radiation from the radiation source through a mask having a series of openings onto a detector surface, wherein the series of openings has a predetermined mathematical relationship among the openings within the series of openings and wherein the series of openings define a mask reference line, to create a mask image having a series of peaks, and having an image reference line within the mask image that can be located and wherein at least 50% of the mask image is projected onto the detector surface; calculating a location of the mask image on the detector surface; calculating a location of the image reference line within the mask image; and calculating the component of the location of the radiation source from the calculated location of the image reference line within the mask image.