Precedent Study 3

Study 3 - Digitally Documenting D-Day: The use of close range digital photogrammetry at Pointe Du Hoc - Richard Burt, Ozgur Gonen

Robert Warden, Vinod Srinivasan

this is a good case study of a project using photogrammetry to digitally document the command post at one of the most historical sites of the D-Day landings: Point Du Hoc. A website will be created for the project allowing an interactive tour. The methods used to collect survey data for both the production of 2d Historic American Building Survey drawings and for the 3D digital model are described.

3D laser scanning - ability to create very accurate 3D representations but the amount of raw data recorded can be unmanageable, especially for outdoor scenes.

Image based modelling techniques - inexpensive and can capture objects of any size. Some systems use computer visual techniques such as computational stereopsis to automatically determine the structure of a scene from multiple photos but are limited by the strength of the stereo algorithms used. Multiple tools/software may have to be used to achieve the desired results., this i am noticing more and more. They speak of a program called Facade which is a research prototype.

An important element to consider is lighting. If the photos are taken at different times of the day, different days, different times of the year, the colours and lighting will not match from photo to photo causing inconsistencies in the final output. These can be altered but slightly to match more but will take some time and skill to match the shadows and highlight. The dark areas make it difficult to identify corners etc ie in a dark room.

Obtaining 3D measurements from the images is done by marking the same point on the building on at least 3 images taken from different positions, and then when sufficient information is collected, computer software is able to locate theta 3D position of the cameras. Once the camera positions are located, a series of calculations locate the position of all marked points and create a 3D model. Below is an example of the workflow.

http://cumincad.scix.net/cgi-bin/works/Show?_id=sigradi2005_634&sort=DEFAULT&search=photogrammetry&hits=37