Syncing cameras with a GPS

I know at least one person has a crazy setup where they have multiple cameras synced with their phone. Any guides for doing this? I'm lucky to have been given a camera ever xmas for 4 years (Contour, Sony Action CAM X2, GoPro) and an iPod Touch so I figured it's time to do some tech work with 'em =D

[video=youtube;CBmz6z0TtBw]https://www.youtube.com/watch?v=CBmz6z0TtBw[/video]
Syncing the video\audio of the multiple cameras is fairly straight forward. Find a reference point that is identifiable on all cameras and line it up. Audio is easiest. I generally use the click of putting the bike into gear to match up the camera feeds.

Getting the data overlay to match up is definitely more difficult. I only did it twice so Jamie might have a better method than me. I use racechrono and it has a built in utility for syncing the data to the video and lets you live preview it with a +/-ms button to adjust. You pretty much have to ballpark it and then watch the video and adjust until it lines up perfect. It will then generate a new video with the overlay in it.

The phone I use on the bike is nowhere near powerful enough to do the overlay on the video so I have to export the session and then load it on my tablet to do the render. It's a bit of a pain in the ***.

^
Is there anyway to start recording on all the cameras hitting one button or are you hitting record manually? I see that racechrono may have support for multiple GoPros but my cameras are all mixed brands. The contour is probably out of the question as it has no way to connect aside from USB.

Great video btw! Are there any other apps you've tried?

I have to start all cameras separately. I'm using two of the original GoPro HD Hero's.

The multiple cameras are edited in a separate program (I use pinnacle studio), and then loaded into Racechrono for the data overlay.

If I recall, Jamie outputs the overlay to a blank screen and then imposes it over his video in premiere. I should probably try doing this as it seems much easier.

I haven't tried Harry's Lap Timer but it is the other big app people use. They work almost the same.