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Author Topic: Forcing the alignment  (Read 2416 times)

Erwan

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Forcing the alignment
« on: November 26, 2015, 08:07:31 PM »
Hello!

I flew with a UAV the Sony a5100 with a 30mm lens set at 1/1000, f/5.6, manual focus. All pictures are geotagged.
Subject : 2 dikes with water around. All the water is masked on all the pictures.
Flight configuration : 1 grid for the orthomosaic and 2 flights around each dike with a gimbal angle set at 45 degrees for the 3D model.

The problem is : I'm not able to align all the pictures... I tried to divide the project in two parts; one for each dike but still not possible.

Printscreen : https://goo.gl/photos/Vmgw5dQNUgyF6t8W8
Picture exemple: https://goo.gl/photos/USY6JBpuittSWgPdA

Thanks a lot for you help!

Erwan

bigben

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Re: Forcing the alignment
« Reply #1 on: November 27, 2015, 02:06:58 AM »
Is that a mask across the top of the photo?  Would be better to use as much as possible for the alignment. Trees may be part of the problem. I don't have a lot of experience with aerial, so while I'm thinking more overlap, most suggestions seem to be fly higher/longer lens. 

I'd love to try: fly lower with a wider lens. Wider lens gives you more cameras per point

James

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Re: Forcing the alignment
« Reply #2 on: November 27, 2015, 11:50:14 PM »
Flying high with long lens, or low with wide lens gives the same 'footprint' on the ground, so for the same flight speed and pattern you get the same overlap and therefore cameras per point.

Trouble with wide lens is that only the 'middle' section of the fov is nadir facing, getting more oblique towards the edges. That means when 'point A' is at the top of the field of view in photo 1 you are looking at it from in front, straight down in photo 2, and from behind in photo 3 when it has reached the bottom of the frame, and in some cases the difference means that 'point A' isn't well matched, if at all, in the 3 consecutive images as its appearance is drastically different from the 3 different angles, particularly when there are complex surfaces such as trees to deal with.

Flying high with a long lens you are always looking straight down on 'point A' in all three photos so it is matched easily, because it always looks more or less the same.

The trouble with the long lens approach is it gives you good XY accuracy but more uncertainty in Z, but still great for orthophotos!

I don't have much experience with aerial either, but this is what I have picked up from the forum anyway!

bigben

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Re: Forcing the alignment
« Reply #3 on: November 28, 2015, 01:23:40 AM »
Oops... had wrong topic open.. reply removed.