PhotoModeler generates the 3D positions of points by projecting straight lines from the camera position, through the point on the film or CCD and out into space. When two such rays are used, the intersection of the rays gives the point position. The following figure depicts this method:
Locating a Point in Space from Two Rays
Representations of two Camera Stations are shown in this figure. Each of these shows the position of the film or the imaging chip and the focal node of the lens at the moment the picture was taken. These representations are simple two dimensional drawings but are sufficient to describe the method.
Assume the user has identified the Marked Point A on photograph 1 and the Marked Point B on photograph 2 as being the images of the same point. PhotoModeler knows where the camera was at the time of the two exposures and it uses this along with A and B’s 2D location in the film plane to calculate the 3D Point location by intersecting the two straight lines.