Here are some tips on how a little trigonometry can help you to improve your drone shoots. Most Virginia drone pilots can fly to a position that “looks right” in their display for taking photos and videos, but what about those large jobs, such as a hundred-acre tract of property?
I recently had a commercial session involving the marketing of 116 acres of undeveloped land. My usual preplanning (and pre-programming the aircraft) was a little more challenging because I wanted to fly at the right altitude, the right speed, and the right camera tilt in order to minimize the “trial and error” approach to videography.
I’ll be happy to talk off-line about the actual formulas, but to keep this post as brief as possible I’ll just outline the principles. The fundamental information you’ll need is your camera’s field of view (FOV) and the frame’s aspect ratio. For example, the DJI Phantom drone’s FOV is 94 degrees and its aspect ratio is 4:3 for photos, and 16:9 for videos.
For 4:3 photos, the trig results are approximately 75 deg horizontal FOV and 56 deg vertical FOV. (Approximate because this is a two-dimensional approximation of a 3-D device.) These results are shown graphically in the figure above. For 16:9 videos, the horizontal FOV is about 7 deg wider (82 deg), and the vertical FOV is about 10 deg narrower (46 deg).
With this information, you can calculate the field of view for any given distance. Say you’re shooting a photo straight down from an altitude of 100 feet. Using the sine and cosine functions, the horizontal FOV is 122 ft and the vertical FOV is 95 ft – or – a rectangle 122 x 95 ft. This is suitable if your subject, say a house, is around 60 ft wide. This ratio stays the same, so at a distance of 200 ft, the rectangle scales up to 244 x 190 ft.
Another useful angle is the tilt required to put the top of the frame just below the horizon. We found out above that the vertical FOV is 56 deg. With the camera’s tilt at 0 deg, the horizon is centered in the view. Therefore, the top and bottom of the view are at 0 deg plus/minus 28 deg. So, in theory a camera tilt of -28 deg should put the horizon at the top edge of the camera’s view. For 16:9 video, the horizon (again in theory) is at about -23 deg. In practice, I use a tilt of -30 deg for photos and -26 deg for videos to ensure landscape pictures aren’t turned into silhouettes by the bright sky.
Another tip: Use algebra to solve the time required to run a certain distance at a given speed. This will help you determine how much air time will be required per run and, thus, how many batteries to bring.
These concepts are approximate and you may come up with different results. Regardless, a reasonably disciplined approach will help you plan your flying sessions.
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