Go Pro for BRUV's??

[daz.p...@gmail.com]

Hey there,

I have a number of Go Pro type camera's and was wondering if I could set them up on a stereo BRUV system. Is this possible and if so what would it involve(cost, software, knowledge, labour etc..).

Thanks for your help,

Darren

[Tim Langlois]

Hey Darren

Using action cams like the Go Pro would be amazing - to make cheap and lightweight stereo systems.

BUT as far as I know the Go Pro's are no good for stereo measurements as they have some hidden image stabilization (or something like that) that gives a false stereo-calibration. 

Apparently when the fish are moving they effectively change length in the stereo image - although the error from the stereo software is still small - so you can't tell there is a problem.

Jim Seager would be a good person to ask about this - and whether he knows of any cheaper action cameras that will work.

Cheers

Tim

[Euan Harvey]

Hi Darren, 

We have doen some tests and the initial results were really promising with great accuracy and precision. So good that we built 3 systems.   However, Jim Seager alerted us to a potential issue when you introduce movement like a diver swimming a camera or a fish swimming through the field of view (or even worse both) which he could see in the imagery.  When we replicated the trials with movement were were getting up to 30% random errors.  The real scary thing was that our RMS and precsion values (our quality control measures we use for telling us when we are making good or bad measurements) did not hold up.  So you don't know when you are making a good or bad measurement.  We don't know exactly why.  It could be an image stabilisation issue, a frame averging issue (which makes sense given the GoPros are designed to make imagery look good).  I have been told that the GoPros (as with many of the cheap cameras) have a rolling shutter.  I haven't figured out what consequence of that could be.  At this time we are recommending not to use GoPros and will continue to trial some of the other cheap cameras.

Euan

 

[Mark Shortis]

Euan,

See   http://en.wikipedia.org/wiki/Rolling_shutter

for a good description of rolling shutters, which effectively scan through the image either vertically or horizontally, rather than capturing the entire image as a full frame.  This is certainly a component of the problems we are seeing with the GoPros, as movement in one area of the image may be distorted or not captured accurately because of the finite amount of time required for the shutter to roll across the image.

The testing that I/we have done on the calibration of the GoPro cameras confirms that there are instabilities present and as a consequence the accuracy of the measurements is compromised.  More testing needs to be carried out, but at the moment I would say that GoPros are not a good option if accuracy is important.

Regards,

Mark.

[Tim Langlois]

Shows how thing have changes in three years!

We are using only GoPro's now (Hero 3+) after we compelted testing that found minimal rolling shutter effect if you use medium FOV and 60 FPS.

And apparently the GoPro 4's are even better.

However, they need a good custom housing to keep them stable for calibration and to allow space for a decent sized battery!

Best

Tim