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The digital camera is by far one of the most common tools for documenting accident and crime scenes all over the world. The low cost, ease of use, and its value as an important communication tool makes it a standard instrument for anyone in Forensic Identification. Even though film cameras are now almost completely obsolete and digital formats are the modern successor, many of the methods and techniques for capturing photographs have remained relatively unchanged. However, with the advent of new software and technologies that have branched out of photogrammetry (i.e. science of getting measurements from photographs), digital cameras are finding new uses as accurate measuring instruments too.
If you haven't heard about Microsoft's Photosynth, you might want to check out this neat little application that is provided freely by Microsoft. Photosynth is a new way of organizing your photos of a particular object or environment such that the photos are spatially oriented with respect to one another. Unlike panoramic images, where you can stitch a number of photographs together to create a 360° image of a scene, Photosynth is a combination of technologies that solve for the common features between photos and how each of the photos are oriented with respect to one another in 3D space. As the images are matched, the camera positions can be calculated and the matching points in each of the images are created as a 3D point.
These "points" define accurate features in 3D space that are common between photos and by taking enough photographs of an object, it is possible to construct a point cloud from the "synthed" images. In effect, this makes it one of the only free 3D scanners that can be utilized to get relative distances between point features of an object.
Although Photosynth was originally intended as a new and creative means of presenting photographs, what makes it technically appealing is that it can solve for the relative spatial relationships between photographs without knowing anything about the camera that took the photograph, and it does it relatively quickly.
The impact of this type of technology is that first responders, forensic technicians, and investigators can quickly gather a large number of overlapping photographs without the need for special targets, expensive equipment, or complicated software. The user just needs to take a lot of photos that cover the object all around and close up (either by physically moving closer to the object or by using a zoom lens). Once the photos are captured, they can be easily processed in Photosynth by a user with little to no training. There are actually very few steps involved in creating a "synth".
However, this simplistic approach is one of the areas where further development is needed since there is little control over the resulting point cloud and there are no integrated measuring tools. The solved points are somewhat a by-product of the technology and currently, exporting the point cloud requires a rather complicated process, (not for the faint of heart). Any post analysis of the point cloud requires the use of third party software for viewing and cleaning of stray points and "noise". (Another possible area of development).
Screenshot from Photosynth online viewer showing a point cloud of a photographed shoe.
Also, one major problem with the structure of Photosynth is that users currently download one part of the software application to their local hard drive, but the photos must be uploaded to a server for viewing on the Photosynth "network". As a result, the default settings make all the "synthed" photos available publicly. There is an option for creating an unlisted "synth", but it does not provide secure encrypted access. Anyone who has access to the URL for the "synth", can get to it. Therefore, security for sensitive investigations is an issue.
Like many other technologies, Photosynth needs to run its course through much validation and testing. One feature lacking is a quality indicator of accuracy or error. Currently, there is a measure that refers to how "synthy" the processed photos are measured in percent (%). Unfortunately, this is really not a useful indicator of accuracy, but it would seem that this could be overcome with some added analytical tools.
Photosynth is still a long way from becoming a tool for forensic investigators, but it would seem this technology could have some benefit in a forensic environment. There need to be specific tools included and certain security measures addressed, but considering how many times a day digital cameras are used to capture and record data at accident and crime scenes, the impact of a product like Photosynth, could be immense.
Above is an image of a footprint in the sand that was taken with a Sony a200 with varying focal lengths (i.e. zoom settings) for many of the shots. There were less than 100 photographs used and they were taken at low resolution (about 2.5 megapixels) just to speed up processing time. Interestingly, the resultant point cloud contained over 168,000 points with color information.
For more information about Photosynth, visit http://photosynth.net/.
Eugene Liscio, P. Eng, is the owner of AI2-3D. A company that specializes in 3D Forensic Measurement and Visualizations. He is a forensic animator and photogrammetry specialist. AI2-3D, Toronto, Ontario, 416-704-2695, email@example.com, www.ai2-3d.com.