As I wrote about in Drone My Roof and Drone My Roof Part 2, I was getting my roof redone at great expense, and I was determined to get a good time lapse of the whole process. As I said in Part 2, I made a circular waypoint track. At semi-regular intervals I went out and flew it twice. My intention was that for each time I flew, I’d use some non-integer number of circles. I wasn’t sure if I’d use 7/8ths of a circle or 9/8ths of a circle, but I thought it would be more interesting that doing one full circle each time. Which is why I did two circles, and also why I had the circles start at the back of the house instead of the front. (Actually, I forget why I chose starting at the back, but because I was going to do a non-integer number of circles I didn’t think it would matter).
For about a day and a half I didn’t think to put starting and stopping the camera into the waypoint file, so there was a bit of a bobble around the back of the house as the drone decided that it needed to turn 45 degrees and possibly move a bit while moving from the end waypoint to the beginning of the next, even though they had the exact same latitude and longitude. I had to edit those bobbles out, to greater or lesser success each time. The last 3 or 4 missions didn’t have the bobble, which was a great relief.
I sped up each clip by 4x, so that it was obvious it was a time lapse. I also added the start time of each clip as a caption.
The other thing I discovered is that even though the drone is tracking 20-odd GPS satellites at once, there were significant differences between different circles. Usually not much between the two circles in one go, but between one mission and the next, sometimes 5 or more meters difference. Which I find a bit odd, because my first gps, a Garmin GPSMAP 195 which only tracked 12 satellites at once, could quite consistently show you which lane you were in when you used it in the car (in spite of it being an aviation GPS). And my Garmin Forerunner 920XT fitness watch could show which side of the river you were on.
As well as the problem with the circles being offset, the center point also meandered around – I had to save a new one several times. Unfortunately the KMZ file only saves center points that are in-use, so you can’t go back to an old one if you save a new one. It’s confusing, because during the session, you can have multiple center points saved, but after you come back to the waypoint file, all the ones that aren’t actually in use are gone.
I did some messing around in Final Cut Pro trying to get something usable out of this. A while ago I used a weird trick I’d found on Reddit’s r/finalcutpro sub-reddit to center a tracked object on the screen, involving inverting the clip, tracking the object, and then applying that to the non-inverted clip. Unfortunately there wasn’t a trackable object in the middle of the roof, so I was wondering if there was a way I could track the four corners of the house and do some sort of geometric mean on that. r/finalcutpro was not much help with that, but suggested I ask in r/vfx but they used a lot of terminology that I didn’t understand. Something about a gaussian splat or something like that.
So I decided on two things. First is that I’d do a single circle each time, starting from the more logical front of the house. Second is that I’d try to hide how badly the waypoint moved around from time to time by using a transition that had a lot of movement in it.
Then as a second attempt, I zoomed in 25 percent, and tried to use the slop to center the images a bit better. I did that by using some guide lines on the screen and setting a keyframe at each cardinal point and moving it as close to centered at each point. But there wasn’t enough leeway in the video – many of the positions I couldn’t get the roof centered without having black bars on the outside.
Not perfect, but I think it’s better than the first attempt.
So lessons learned:
- Make the waypoint file go full circle or maybe two circles without stopping, starting at the front of the house.
- Make the circle further out or use a wide angle lens so there’s more slop on the edges for cutting in.
- I think I’d fly slower and speed it up more – I like the frenetic movements. I know I said in Part 2 that I didn’t like it that way, but I’m having second thoughts.
- Be more careful about launching the drone at exactly the same place each time – some of the worst offsets were the times I had to launch at somewhere other than the exact spot on the sidewalk I’d chosen for most of them. In one extreme case I had to take off the screen window and fly it out the door.