If the user of PhotoModeler takes the following precautions, the errors will be minimized and measurement accuracy maximized:
• ensure that a well-calibrated camera is used for the project,
• maximize the number of photographs that each point is marked on,
• ensure that all points appear on three or more photographs,
• minimize the number of points that appear on only two photographs,
• ensure that the angle between the camera positions is as close to 90 degrees as possible,
• make sure the project has at least 25 points and the photographs have good coverage,
• ensure all point and line markings on the images are precise, and
• do not guess at a point location if it cannot be seen, is not distinct, is fuzzy or is hidden by some other object.
The highest level of accuracy can be achieved by using man-made targets and the program’s special sub-pixel marking algorithms. These targets are typically high contrast circular dots. Also refer to the section Using Targets.
Our tests to date indicate that PhotoModeler is comparable in accuracy to most film-based small-restitution systems and other 3D triangulation equipment. PhotoModeler with sub-pixel target marking can be comparable in accuracy to high quality theodolites and total stations.