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 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
or scene. It is the
intersection of these straight lines, a process of triangulation, that determines the three-dimensional
location of the point of interest. 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 site 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 the 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 instead of a survey of the site..
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, can be
located with precision.
The coordinates are then plotted on a two
dimensional overhead diagram or rectified aerial photograph. 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 with 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.
Close Range
Photogrammetry Demonstration Using Aerial Photos
A demonstration of the use of close range
photogrammetry in preparing an aerial photo exhibit of a large intersection.
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
