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Author Topic: Scanning a water body  (Read 12730 times)

George

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Scanning a water body
« on: July 06, 2012, 01:43:37 AM »
Hi,
I am aiming to obtain a number of aerial pictures of a water body (sea or lake). Water is not a constant environment - it is just chaotically moving.
What are the recomendations  for that case (may be in terms of shooting the object or something else) and how does Photoscan tolerates moving objects or surfaces, where, actually, no objects to get hooked on?
Thanks

Alexey Pasumansky

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Re: Scanning a water body
« Reply #1 on: July 06, 2012, 11:24:06 AM »
Hello George,

There was a similar topic already: http://www.agisoft.ru/forum/index.php?topic=526.0
maybe you'll find something useful there.

Objects that changes their shapes are not good for PhotoScan. Especially water, since it could be also transparent.
For getting good orthophoto results containing large water surfaces you can cut the water area (usually it is very noisy) from the model and than use Fill holes tool, since masking is not always possible for large amounts of data.
Best regards,
Alexey Pasumansky,
Agisoft LLC

George

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Re: Scanning a water body
« Reply #2 on: July 06, 2012, 03:33:37 PM »
That is, actually, the thing.
We are exactly after the water body itself and may be after the objects under the water.
Could then, for example, help the presence of a land in the pictures or other stable objects? Or it is still the problem for Photoscan?

Alexey Pasumansky

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Re: Scanning a water body
« Reply #3 on: July 06, 2012, 03:43:56 PM »
Hello George,

Then there are two general cases:
1) if the water is unclear and not enough transparent - you'll get very bad result.
2) if the water is very clear and transparent, there's a chance you'll get the water bed reconstructed, but with the distortions related to the refraction.

We have some requests concerning bathymetic application of the PhotoScan, but it is not in our short-term planes.
Best regards,
Alexey Pasumansky,
Agisoft LLC

fpbv

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Re: Scanning a water body
« Reply #4 on: July 06, 2012, 04:05:20 PM »
Alexey

Did you said for bathymetric solutions???
I?ve been looking for this for the last week for a client and I am very interested on this kind of solution.
I hope to hear more about this.

Thanks!

andyroo

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Re: Scanning a water body
« Reply #5 on: July 09, 2012, 03:30:37 AM »
I am regularly imaging a river corridor with two lakes, and have been dealing with this a bit. My best results are from masking the water or cutting it out, then filling holes. changing reflection on flat water, and bad matches on white water are common, so the surface is noisy, not very useful, if at all. You can use the amplitude of the noise to filter the water surface out - I have been limited to doing that with the processed DSM, though I am hoping I can figure out how to write a filter in meshlab.

The water I am working with is very turbid, so I haven't tried extracting bathymetry through the water surface, but I have found that you need a fair amount of land surface on at least one side of the water body to be able to generate matches. On forested areas it is the most challenging, since the relief is great - and it is better to have at least 60% overlap along track, with at least 30% of the across-track image showing shoreline in my experience.

fpbv

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Re: Scanning a water body
« Reply #6 on: July 09, 2012, 04:15:41 PM »
Andyroo

I did a river a couple months ago and to have fully working I did 70% overlap along track and 30% across-track.
My only problem was I did the mask on the river but it didn?t close the hole on the river.

datapolo

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Re: Scanning a water body
« Reply #7 on: July 11, 2012, 02:51:27 PM »
fpbv, what kind of water body do you want to measure the bathymetry of?

Mike

George

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Re: Scanning a water body
« Reply #8 on: October 15, 2012, 03:14:18 PM »
... cut the water area and fill holes? Please explaine.

Hello George,

There was a similar topic already: http://www.agisoft.ru/forum/index.php?topic=526.0
maybe you'll find something useful there.

Objects that changes their shapes are not good for PhotoScan. Especially water, since it could be also transparent.
For getting good orthophoto results containing large water surfaces you can cut the water area (usually it is very noisy) from the model and than use Fill holes tool, since masking is not always possible for large amounts of data.

Alexey Pasumansky

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Re: Scanning a water body
« Reply #9 on: October 17, 2012, 01:09:57 PM »
Hello George,

I mean that it is possible to remove manually faces from the water bodies, then fill up the empty spaces using Close holes feature from Tools menu.
Best regards,
Alexey Pasumansky,
Agisoft LLC

George

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Re: Scanning a water body
« Reply #10 on: October 17, 2012, 01:12:18 PM »
so that is manual work. I am little bit concerned if it is possible to do accurate enough
Then another thing about Close holes - it closes the rest as well and I would say not in the way I want