PHOTOGRAMMETRY

     Photogrammetry is used in many different fields including topographic mapping, engineering,
     archeology and police traffic crash and crime scene investigations.

     It is a measurement technology in which the two or three-dimensional coordinates of various points on
     an object are determined by measurements made from the photographic images. These may be
     points on a vehicle to determine a crash damage profile or points on the ground at a crash scene
     such as tire marks, gouges and scuffs.

     Common points are identified on multiple photographic images. A line of sight can be constructed
     from the camera location to the point on the object. It is the intersection of these straight lines, a
     process of triangulation, that determines the three-dimensional location of the point of interest. More
     sophisticated algorithms can exploit other information about the scene that is known in some cases
     allowing reconstructions of 3D coordinates from only one camera position or cameras with unknown
     settings (inverse camera).

     A typical traffic crash case involves a number of photos taken of the crash scene by the police. The
     police camera is not metric, or calibrated with known settings, for photogrammetric analysis. The
     photogrammetrist will visit the scene and, using a metric camera, obtain calibrated photos. These
     calibrated photos will include objects that can be seen in the police photos and are still on site, such
     as utility poles, roadway markings, traffic signs and fence posts. These objects will be used to
     determine known coordinates across all available photographs. Alternatively, these points can be
     coordinated using any accurate survey method, such as total station. Very often, for traffic crash
     scenes, calibrated low level aerial photographs will be obtained.

     With this information, using the inverse camera process for the police photographs, the locations of
     tire marks, gouges, police photographer positions and other points of interest seen only in the police
     photos and no longer at the crash site.

     The coordinates are then plotted on a two dimensional overhead diagram. In some cases, the
     police photos and aerial photos can be combined and rectified to provide an overhead view of the
     crash scene.

     Harris Technical Services utilizes photogrammetry in the analysis of many accident cases utilizing
     high resolution aerial and ground photos of the accident site. We perform "forensic camera" analysis
     to determine a scene photographer's position and the locations of objects and view obstructions that
     are no longer on the scene.

     Photogrammetry software, Photomodeler, is available from Eos Systems, Inc. Training courses, under
     contract from Eos Systems, Inc., are available from DCM Technical Services.
     
     Semi-Automated Crush Determination Using Coded and Non-Coded Targets with
     Close-Range Photogrammetry
     Dan C. Mills
     DCM Technical Services
     Toronto, ON

     Vehicle crush measurements have typically been done using either offset methods or punctual survey
     methods such as with a total station or using photogrammetry. Using a total station to complete
     crush measurements around a vehicle can yield accurate measurements along all 3-axis but will
     require multiple station set-ups to traverse around a vehicle. Using photogrammetry to determine 3-D
     deformation of a vehicle can result in the accuracy of a total station with only one operator and allows
     the versatility of measuring any number of points at any time using the available photographs.

     Accuracy Study Project of Eos Systems� PhotoModeler
     Klaus Hanke, Associate Professor  
     University of Innsbruck, Austria

     One Part in 300,000 - Precision and Accuracy Discussion
     Alan Walford
     Eos Systems Inc.

     Project Demonstrations of Vehicle Crush and Skid Mark Mapping
     Eos Systems, Inc.
     Vancouver, BC