A few weeks back we wrote a blog on modifying GoPro's for use in drone ag imaging. If you recall from that blog, there were a couple of open issues with the GoPro:
- We couldn't set the clock accurately because there is no GPS on the GoPro.
- The images using the 2.97mm lens from Peau Productions wouldn't stitch with Agisoft Photoscan Pro.
We've solved those two problems, but have identified another that might be a show stopper for using the GoPro.
Setting the time: We found that the GoPro downloads the clock time from the iPhone or the iPad when it is connected via WiFi. Most of the time this happens automatically, but if not press the little wrench icon on the i-device, then scroll down to "Set Date and Time." Then the trick is to make sure the i-device has the correct time. In IOS, if you set the Settings/General/Date & Time to "Set Automatically" you might think that this would set the time automatically -- but you would be wrong. Unfortunately you'll need to toggle the "Set Automatically" switch on and off. To make sure it is really done correctly, we suggest that you download an atomic time app. We find that the GoPro's drift between 1 and 3 seconds per day so this is something you'd need to do every day. So -- this works but we're trying to make the work flow as simple as possible and it adds a bunch of steps. (BTW, we haven't tried it on Android devices but the process is probably similar).
Image stitching problems: We bought two 4.14mm lenses from Peau Productions -- one with the regular IR-cut filter and one "NightVision" model (i.e. no filter). Then we installed the Event38 red-notch filter as we described in the previous blog post. We're happy to report that all the "squigglies" we saw last time have gone away. Here's a zoomed-in example of our model airfield. It doesn't have the nice straight lines of row crops but you'll get the idea:
A vibration mount is pretty important for use on a multirotor. There are lots out there, but this one from DJI works well for us and isn't expensive.
So, we're happy campers, right? Actually no -- the GoPro has a HUGE problem that at the moment will keep us from using it. Namely, we can't set the shutter speed. On bright sunny days the shutter speed will be high enough, but on overcast days it drops as low as 1/60th. With our planes flying around 15m/s we really need to keep the shutter speed up around 1/1000th to obey the rule of thumb of not moving more than one half a pixel while the shutter is open. So if anyone knows how to hack the GoPro firmware, we're all ears!
In closing, we are working on another solution but it's still too early to discuss. We'll have another blog post on it in a month or two.