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Author Topic: Photogrammetry - Sphere-like effect on the ground and no accuracy  (Read 4533 times)

dyrvar

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I am new to the forum, so please correct me if this post is not where it belongs or if more information is required.

A set of images have been collected using a DJI UAV over a farm field. The farm field has a hill from the north almost to the middle of it. From the middle to the south it is more or less flat.

The model below has been rendered using 25 images with 21 GCPs. There are more photographs, but 25 are used just as a proof of concept. The expectation was to receive a some-what accurate model, but in fact it is completely wrong.

The UAV has taken the photographs from a 130m elevation from the starting point, which itself was at around 103m elevation from sea level (using GPS to measure).

On the images below the view is from the West, so on the left of the images is North (should be a hillside) and on the right is South, should be flat. Instead PhotoStan Professional 1.0.4 is rendering the model as if it's curved, part of a sphere.

http://smilyanp.com/huma/downloads/Simpsons_farm_drone/Test1_Cloud.PNG



http://smilyanp.com/huma/downloads/Simpsons_farm_drone/Test1_Texture2.PNG



Has anyone experienced similar problems, do you have an idea what has been done incorrectly?

ppkong

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Re: Photogrammetry - Sphere-like effect on the ground and no accuracy
« Reply #1 on: August 05, 2014, 08:30:18 AM »
Did you try to use the "Optimize" option to optimize the results of align photo?

David Cockey

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Re: Photogrammetry - Sphere-like effect on the ground and no accuracy
« Reply #2 on: August 05, 2014, 02:46:51 PM »
I had a similar problem with a long strip of photos. The photos taken with a camera/lens with relatively high distortion, and there was just enough overlap for the photos to process. No GCP's.

My hypothesis is the minimal overlap resulted in the PhotoScan lens correction being slightly in error, and accumulation of the error along the strip resulted in the curvature.

You may need more photos with more overlap.

Santiago

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Re: Photogrammetry - Sphere-like effect on the ground and no accuracy
« Reply #3 on: August 05, 2014, 05:21:43 PM »
Hi dyrvar,

I think what you're seeing is the bowl effect. What's the accruracy of the GCP's you're using? This might be the cause of the bowl effect you're experiencing.

Please check this link for a solution. hope it helps.

http://www.agisoft.ru/forum/index.php?topic=600.0

Best,

Santiago

Alexey Pasumansky

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Re: Photogrammetry - Sphere-like effect on the ground and no accuracy
« Reply #4 on: August 06, 2014, 10:38:51 AM »
Hello dyrvar,

I also recommend to use marker-based optimization to fix the bowl-effect.
Best regards,
Alexey Pasumansky,
Agisoft LLC