Calculating Vehicle Speed from Video Evidence Webinar Series

This video was recorded from the webinar on May 30, 2024.

Determining Vehicle Speed from Video Evidence

Video evidence is often used to calculate vehicle speed in forensic investigations, but investigators must be diligent in the details. In this 30-minute webinar, Automotive Engineer and the head of the Technical Services group, Marcus Mazza will walk attorneys through the forensically sound processes used for determining vehicle speed by video.

Transcript Excerpt

This technique is called camera matching and reverse projection.

In this case, we're going to use a commercially available software program called Photo Modeler.

There are others on the market. Photo Modeler is one of the ones that we use here at Robson.

Photo Modeler is going to use three-dimensional scan data of the area to backwards calculate parameters for the camera. So we're going to give it positional data from this laser scanning that we did of the area. And the software is going to determine the position of the camera, the focal length of the camera.

If we have enough data points, we can also determine lens distortion of the camera.

And all of those parameters are going to be calculated and then allow us to reverse project or project images back into the frame as seen through the lens of the camera, and then we can position those objects until they overlay on the actual objects seen in the video in order to determine their positions. I know that sounds really confusing, but I think once we lay it out here and go along, it'll make a lot of sense.

So the first step is we take our three-dimensional scan data, and we pick a number of control points, and we use that to basically solve for the camera. What does that look like? Well, once we're done, we can take that laser scan data, reverse project it back onto the frame that we have here from the video to take a look and see how well were we able to match our camera.

I'm going to go through these slides forward and reverse so you can kind of see the transitional effect. So this is the video frame that we see here unaltered, and then we're going to slowly overlay our laser scanned data, which is three-dimensional point data taken using, in this case, a Leica laser scanner, and we're going to overlay it. So now you can see that we're basically looking at laser scan data. And as we back up, we're looking back at the video frame.

So you can see that we have a pretty good fit. Our telephone poles line up, our building here in the background, our, our sign in front of our lab.

You can see that fences, road, everything seems to visually line up well. The software will also provide us with a mathematical, representation of how well it was able to fit the data.

But, again, we always look at this visually to ensure that our visual fit is what we expect. Once we have this fit done, we can now take this information that we process then and determine for the camera, and we reverse project in data. In this case, we're going to take laser scan data of the truck in question, and we're going to take that laser scan truck, project it back into the image or back into the frames of the video, and we're going to move it around in three-dimensional space until it lines up with the positions we see in the video frames.


Marcus A. Mazza, Automotive Engineer & Crash Expert

Marcus A. Mazza, P.E.

Automotive Engineer & Crash Expert
Marcus Mazza is an automotive engineer with diverse experience in production vehicles, military vehicles, and motorsports. He applies his expertise to intellectual property disputes as well as vehicle… read more.

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