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Author Topic: Best practices for tank scanning  (Read 21949 times)

bigben

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Re: Best practices for tank scanning
« Reply #30 on: March 27, 2015, 07:07:59 AM »
But I don't think it helps taking 5 shots that have a lot of overlap.

Unless you use a pano rig and group the images as a camera station...

Marcel

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Re: Best practices for tank scanning
« Reply #31 on: March 27, 2015, 02:28:43 PM »
But I don't think it helps taking 5 shots that have a lot of overlap.

Unless you use a pano rig and group the images as a camera station...

I haven't used the camera station function myself, but I assume it treats all shots in the camera station as a single panoramic photo?

I can't see how it would be useful to have 5 shots at the same position with 80% overlap. You are not adding more information compared to 2 shots with 20% overlap. (even more so when using a pano rig where there is no parallax at all).

Alexey Pasumansky

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Re: Best practices for tank scanning
« Reply #32 on: March 27, 2015, 02:30:41 PM »
From one camera station it would not be possible to reconstruct a 3D model, as the depth information cannot be extracted for such configuration. But if there are multiple camera stations in the project, it would be possible to get a 3D model of the scene.
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Alexey Pasumansky,
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uuderzo

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Re: Best practices for tank scanning
« Reply #33 on: March 27, 2015, 02:38:59 PM »
Alexey, is the camera station used to simplify the alignment process to PS?
Just to say to it not to bother aligning in space all pictures from the same camera station?
And if so, does PS still handle little offsets that may occur in the shots of the same camera station?

Thanks! Umberto

Alexey Pasumansky

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Re: Best practices for tank scanning
« Reply #34 on: March 27, 2015, 02:43:07 PM »
Hello Umberto,

PhotoScan assumes that all images in the camera station group are taken from exactly the same camera position, so using nodal head is recommended. Offsets would not be compensated and may lead to the reconstruction problems.
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Alexey Pasumansky,
Agisoft LLC

uuderzo

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Re: Best practices for tank scanning
« Reply #35 on: March 27, 2015, 02:44:32 PM »
Thanks for the clarification Alexey!

bigben

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Re: Best practices for tank scanning
« Reply #36 on: March 27, 2015, 04:11:09 PM »
With a camera station you technically don't need to have overlap between images in the same camera station... but it certainly helps.  The advantage is that it calculates the position of all cameras from a wide range of angles, providing a more accurate camera position.  If you have enough offset to create a stereo pair then you have too much offset to define a camera station and it's possible that the alignment may fail miserably... but with a properly set up pano head you can get very clean point clouds.

Marcel

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Re: Best practices for tank scanning
« Reply #37 on: March 27, 2015, 07:08:53 PM »
I still don't see how having 5 images with 80% overlap helps. Please see the attachment of what I mean with 5 shots vs 2 shots.

Especially when using a panorama head, the 3 extra images will have the very same information. There is no extra useful information for Photoscan to reconstruct anything?

bigben

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Re: Best practices for tank scanning
« Reply #38 on: March 28, 2015, 12:26:05 PM »
Especially when using a panorama head, the 3 extra images will have the very same information. There is no extra useful information for Photoscan to reconstruct anything?

It wasn't so much the overlap I was refering to, as the fact that multiple images with lots of overlap = very similar positions.  Instead, taking 5 shots from exactly the same position (a camera station) and spreading out the camera rotations (giving you a wider field of view) does provide a benefit for accuracy.

I've attached a schematic drawing that shows what I mean about positions. Photoscan can get more information from a photo when the camera position is different (instead of only the angle being different).

This is the case if you load all of the images separately into Photoscan, but if you 're using camera station groups you may find the reverse provided you still have an adequate number of camera stations.

Wishgranter

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Re: Best practices for tank scanning
« Reply #39 on: March 29, 2015, 03:05:29 PM »
tarkhilIf still can go to the tanks can guide how precisely can capture them.. contact me over PM...

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FoodMan

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Re: Best practices for tank scanning
« Reply #40 on: March 29, 2015, 06:44:55 PM »
hey Milos.. hehe mini writing is kinda fun :)

Marcel

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Re: Best practices for tank scanning
« Reply #41 on: March 29, 2015, 09:26:42 PM »
tarkhilIf still can go to the tanks can guide how precisely can capture them.. contact me over PM...



Why not post some tips here, that way everybody benefits?

Wishgranter

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Re: Best practices for tank scanning
« Reply #42 on: March 29, 2015, 11:36:22 PM »
Heheh have not seen that is so small....

Marcel, trying pickup people that need a bit guidance, not interested to share it in the "wild"..... 
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