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Old May 22, 2013, 08:52 AM
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Pass1's Avatar
Saudi Arabia, Makkah Province, Thuwal
Joined Aug 2012
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Does anyone use structure from motion?

Hi all,

I have been asked to gather data for a UNESCO world heritage site (it will be restored and they want before/after). The request has come straight from the government, and before we head out and do all the flying we have been practicing at my University's campus.

I have attached a video of a sample of the data that we are collecting, as you will see is a 3D point cloud, and we visualize it in our 3D environments (what you see in the video is just one eye).

I was wondering if anyone has experimented with this and found the sweet spot... there are many degrees of freedom (altitude, speed, angle of the camera etc...) and we are experimenting with all of them... but it is quite tough!

So far we have noticed that <10Km/h at about 50m - 75m altitude with the camera about 45deg is a good compromise, but more experimenting is to be done!

Would love to hear from your experiences!

Reconstructing urban areas with a quadcopter flown FPV (1 min 37 sec)
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Old May 22, 2013, 05:47 PM
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Wright's Avatar
King, NC
Joined Aug 2000
460 Posts
Hummmm... big topic. We do sfm and generate DEM's from images taken from a canon T2i dslr. Typically we fly at 60 m AGL moving at 6 m/s with camera pointed straight down. We fly 150 to 250 m transects spaced at 20 m. This gives us the required overlap (40 and 60%). We then use Palentier to create geo tagged images and then take those to Agisoft photoscan to make mosaics. Any further processing goes to ENVI. It's a very complicated process and does not always work. We have a very talented undergrad doing the work. Here are some small jpgs of an island we did this spring.
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Old May 23, 2013, 01:57 AM
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Saudi Arabia, Makkah Province, Thuwal
Joined Aug 2012
164 Posts
Interesting, what focal length do you use?

I am assuming you are not interested in the faces of the buildings?
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Old May 23, 2013, 07:05 AM
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King, NC
Joined Aug 2000
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We use 24 mm with stabilization. Right, we do grassland and forest canopies (every image looks the same). Agisoft does not handle hard edges as well as you might think.
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Old May 23, 2013, 08:38 AM
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Saudi Arabia, Makkah Province, Thuwal
Joined Aug 2012
164 Posts
Yes, we noticed that! We are primarily using VisualSFM and we are much happier with the results!
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