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Author Topic: Problem with align of forested images  (Read 3217 times)

Magrim

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Problem with align of forested images
« on: June 20, 2018, 10:19:51 PM »
Hello

I'm working with forested areas, but the images not aligning. The flights that are in trouble were made at 60 meters of altitude and 80% of overlap, where only as border areas are recognizing homologous points. I made a new mapping at 70 m altitude and 90% overlap, where I got a better result but it is not 100% yet. I would like help solving this problem, I already tried to include markers manually but I didn't succeed. Is it possible to correct the other orthomosaic from this second that I get a better result? I tried to import a sparse cloud as a text file too (markers).

bgroff

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Re: Problem with align of forested images
« Reply #1 on: June 21, 2018, 12:42:43 AM »
From my experience, (dense) forested images cannot be aligned because there are not enough features to identify Tie Points. It is not unique to PhotoScan. I have the same issue with any image set that includes featureless images.

rossnixon

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Re: Problem with align of forested images
« Reply #2 on: June 21, 2018, 05:38:59 AM »
Hello

I'm working with forested areas, but the images not aligning. The flights that are in trouble were made at 60 meters of altitude and 80% of overlap, where only as border areas are recognizing homologous points. I made a new mapping at 70 m altitude and 90% overlap, where I got a better result but it is not 100% yet
We work with forested areas and get good alignment when flying about 6700 feet above ground. Using a Canon EOS 5D Mark II via a mount in a small aeroplane.

outsider

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Re: Problem with align of forested images
« Reply #3 on: June 22, 2018, 02:12:20 PM »
There is a HUGE difference between what a camera will see from 2000m (6700 ft) and 60m.

If the trees sway randomly by say 1m, from 2000m that movement is invisible, where from 60m, that movement is quite significant!

To the OP,  you need a higher altitude or a day that has zero wind, in order to accurately capture trees.

jmos

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Re: Problem with align of forested images
« Reply #4 on: June 25, 2018, 08:48:43 AM »
Using our Phantom 4 Pro we typically fly 120m above ground.

If its an open canopy and not to dense we can get away with 80 forward 60 side overlap.
If its closed canopy we fly 80/80 even 90/90 for Karri Regrowth SW Western Australia.
And yes try to fly on calm days/no wind


ManishSahu

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Re: Problem with align of forested images
« Reply #5 on: June 26, 2018, 08:25:51 AM »
Yes, In case like these it is very difficult to extract feature and match them.
Although try aligning photos with lowest accuracy. This will increase some of the matches and you might get correct photo alignment

Krzysztof

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Re: Problem with align of forested images
« Reply #6 on: June 26, 2018, 01:50:21 PM »
From our experience increasing overlap won't help.
If we spot some forest areas while flight planning we usually plan another flight with higher level.
Ex. base flight at 60meters and another above forest at 250-300 meters. Then we combine these two sets of photos in agisoft. You won't lose as much accuracy - I think 5-6cm GSD at the tree is still very accurate ;).