How to do digital overlays

There has been a boom of cyclists that have started to take to the roads with video cameras. As one of them, I try to come up with and promote ways that we as a group can make our videos better. One thing that is missing from the videos is speed, and with wide-angle lenses it can often be very difficult to judge from a video just how fast a cyclist is actually traveling.

I’ve made a few videos where I have digital read outs on the video and I often get questions asking about these when I make them.

A cyclists who goes by the name VeryMadMart has made a java application that takes the files recorded by a ContourHD and the TCX files recorded by a Garmin GPS unit and puts the data on the video frame by frame with some nice graphics.

Essentially the application just needs a .mov file and a GPX file to make the overlay, so you don’t have to use a ContourHD and Garmin device.

The hardest part of doing this is trimming the video and editing the TCX XML file to match. Essentially most of the time the video and data will be slightly out of sync. I have found the best way is to use the latitude and longitude found in the XML and search that on google maps, it gives me an idea of where I’m looking at and I usually cut the start of the video to a side road or similar where I can easily match it up ‘exactly’ on the google maps. This minimises the delay from video to data to within a second in most cases.

This isn’t the only way cyclists can do this. Vholdr, the owners of the Contour brand, have released a version of their camera with GPS inbuilt to it. This makes for another way to get some information about your ride and match it up to your camera. How this works with a site like youtube I don’t know. But upload the footage on to the Contour website and it looks like the whole thing is automatic and a nice map and data is displayed next to the video.

Digital overlays and speed readouts isn’t just a gimmick, in the case of a collision the information will be vital. GPS positioning will back up what your camera says and gives you an accurate speed just before impact! No more ‘I was doing about 15mph officer’
How many motorists can do this? I bet less than 1% can!

For more detailed information on the steps involved and to download a copy of the java file, please visit VeryMadMarts website.

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5 thoughts on “How to do digital overlays

  1. Given that a GPS receiver is hooked up to 5+ atomic clocks in low earth orbit, it’s the time you should trust -and the contour should get its timestamp from the computer. If the two are out of sync its your computer that’s got clock problems. Either set up the time sync to work against an NTP server that seems to be in sync with your GPS, or (somehow) set the computer to get its time from the GPS unit. That would be best way.

  2. I hope to get GPS on my next camera, like the Contour or ATC9k cameras that have them built-in now. I’m curious if they match up GPS data points with image frames, or can be matched up with a shared timestamp, in order to solve the sync problem. I definitely hope to write some overlay software for some impressive looking overlays once I get such a camera!

    • I would stay away from an ATC cameras, they are far from the best and not worth their money imo.

      I’m trying to get my hands on a ContourHD GPS unit to test it out! I’m not quite sure of the options with doing your own stuff or how it saves the GPS data.

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