Experience at different speeds with Phantom 3

I know that when I fly a tract at 10 m/s at 40 meters high with the phantom 3 I get horizontal distortion in my pictures. I also know that if I do the same thing but at 5 m/s I don't get any horizontal distortion. Has anyone else played with the settings more to see where the sweet spot it?

Neil Atkinson September 15, 2015 22:04

Official comment

On a rolling shutter camera (like the ones on DJI drones and GoPros) each line gets exposed at one time and then read out of the sensor. Then the next. Then the next... From top to bottom.

If you are flying forward at 10 m/s at a height of 40 m, your spot length is 51.86 meters and at 30 fps, the frame time is 33 ms. In 33 ms you travel .33 meters. That means that the distance from the first line that is exposed to the last line of the frame being exposed is 51.53 meters or a .6% difference in length. That is more than enough to mess up a lot of reconstruction calculations.

Numbers are from www.mapsmadeeasy.com/flight_planner

This effect shouldn't cause any horizontal distortions in the images since the change occurs along the path of travel.

Previously, when our app was flying forwards on the way out and backwards on the way back, we were getting some really weird calibration results due to the fact that we were compressing the images linearly on the way out and expanding them on the way back. We have changed the flight planning now so at least the badness is consistent.

If you really need accurate data with a DJI aircraft, you will need to fly pretty slow.

Tudor September 16, 2015 16:08

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5 comments

We make every attempt possible to make sure all the images are taken at the same speed so the effect will at least be consistent. That is why we added the slow down, turn around and acceleration areas outside of the survey boundary.

This was more to address speed induced image spot deformation but we hadn't seen anything horizontally in the image.

Have any good examples to share?

Tudor September 15, 2015 23:57 0 votes

I don't have these overlayed in you library, but https://www.mapsmadeeasy.com/maps/public/b347676f31ec458193d662829a4469d8 and https://www.mapsmadeeasy.com/maps/public/cbd8958a267e46e993d285494d9bce8d are of the same property. One is at 10 m/s and the other is at 5. If you try overlaying them the first map is stretched with the length of the property. If I have time tonight I'll try uploading them as an overlay.

Neil Atkinson September 16, 2015 00:18 0 votes

I've flown at 10 m/s, but was at 60 meters height and did not notice any distortion. I'll try a 40 meter test and both speeds this weekend to see if I see much difference.

Kurt Bantle September 16, 2015 11:58 0 votes

yeah I reflew the same site several times today at different speeds and heights. The errors were minor (and were probably more likely to be calibration errors). The app won't actually fly 10 m/s at 40 m. Is this a new feature? I could swear that the first few missions I flew it got up around 30mph. Anyway, I'm feeling more confident in the data I'm getting. I think the fix you mentioned earlier did wonders.

Neil Atkinson September 17, 2015 03:03 0 votes