There are three central tenets that PhotoModeler depends on to do three dimensional measurement:
• PhotoModeler assumes that a ray of light coming from some point through the focal node of the lens of a camera and hitting the film can be described by a perfectly straight line.
• By knowing where the camera was at the time of exposure, PhotoModeler can use the location of where the ray of light hit the film to calculate the equation of that ray of light in three dimensions.
• Each point that is to be measured is imaged in at least two photographs, and preferably in three or more. These points are used to compute light ray positions and their intersections for determining positions in three dimensional space.