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Author Topic: low accuracy align produces better results than high accuracy  (Read 10471 times)

jeremyeastwood

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low accuracy align produces better results than high accuracy
« on: September 15, 2015, 02:25:56 AM »
Hi there,

I aligned a large set (450) of photos using the low accuracy settings (reference pair selection, 0 tie point limit, 100,000 key point limit), producing a nice alignment and ultimately a good orthomosaic:

https://www.dropbox.com/s/a9893zd1roww822/Screenshot%202015-09-14%2016.09.31.png?dl=0
https://www.dropbox.com/s/c4cu5cmny295is6/Screenshot%202015-09-14%2016.12.23.png?dl=0

however, when re-running using the high-accuracy settings for align (other settings the same), some of the photos aren't stitched, leaving large holes in the map:

https://www.dropbox.com/s/2b1lzwg7jb8fxvx/Screenshot%202015-09-14%2016.23.48.png?dl=0
https://www.dropbox.com/s/rn45kzdly9ntvfu/Screenshot%202015-09-14%2016.24.17.png?dl=0

Any ideas what's going on, or what settings I might be able to use to improve the results of the high-accuracy alignment (or should I use low-accuracy align as a default instead)?

Thanks

dcm39

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Re: low accuracy align produces better results than high accuracy
« Reply #1 on: September 15, 2015, 11:02:23 AM »
I've often found this to be the case too. I believe this is to do with the scene texture and the length scales of that texture. Using lower accuracy settings forces the software to only use much "larger" features in the image, which may be more stable if the small scale features are very uniform.

One way I get round this is to run the model at low accuracy, and georeference it and save the estimated camera locations and orientations.  Then I re-run at high resolution having imported the prior orientations as the initial parameters (with control based pre-selection).

However, if "low" accuracy alignment is sufficient for your project, I'd probably just stick with that.

Wishgranter

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Re: low accuracy align produces better results than high accuracy
« Reply #2 on: September 15, 2015, 01:09:01 PM »
set 40k  and 10k in preselection and get GOOD results on HIGH,  trying to detect  HIGH  point value will force to use even "weak" points = worse results.. try it and report back
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Herman

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Re: low accuracy align produces better results than high accuracy
« Reply #3 on: September 15, 2015, 09:44:50 PM »
Hi

I have a similar problem on a rather large photo set 11500 images , a big portion is desert landscape with few features ,
but we still have a very high success rate with only 30 images not aligning - see attached image.

Any suggestion to include these images with re-aligning all 11500 images?

Regards
Herman

jeremyeastwood

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Re: low accuracy align produces better results than high accuracy
« Reply #4 on: September 15, 2015, 11:23:04 PM »
Thanks for the responses guys - very helpful.

@dcm39 that's very interesting - I believe the medium / low accuracy settings downscale the images before alignment, so that would be eliminating some of the smaller features.  An interesting approach for some homogenous imagery with small feature scales, although after running a lot of different jobs through low and high accuracy alignment I've more often found the low accuracy settings to provide worse alignment (more holes).  This could be a backup approach for when the high quality alignment fails, so will keep trying in the future.

@wishgranter great recommendations - using 40k key and 10k tie worked a charm:
https://www.dropbox.com/s/qm4urtq58sleovb/Screenshot%202015-09-15%2013.05.54.png?dl=0
https://www.dropbox.com/s/rw6az0a81ib70ho/Screenshot%202015-09-15%2013.06.07.png?dl=0
are these settings appropriate across all camera models / scenery types?

Thanks again guys

jmgc

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Re: low accuracy align produces better results than high accuracy
« Reply #5 on: September 16, 2015, 02:51:00 PM »
Hi

I have a similar problem on a rather large photo set 11500 images , a big portion is desert landscape with few features ,
but we still have a very high success rate with only 30 images not aligning - see attached image.

Any suggestion to include these images with re-aligning all 11500 images?

Regards
Herman

Hi Herman,

Select the unaligned images. In the Reference Pan choose one of those selected images, right-click and choose "Align Selected Cameras".
Sometimes it works.
José Miguel Campos
Geospatial Specialist
UAS Operations Manager

Wishgranter

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Re: low accuracy align produces better results than high accuracy
« Reply #6 on: September 17, 2015, 04:27:05 PM »
Thanks for the responses guys - very helpful.

@dcm39 that's very interesting - I believe the medium / low accuracy settings downscale the images before alignment, so that would be eliminating some of the smaller features.  An interesting approach for some homogenous imagery with small feature scales, although after running a lot of different jobs through low and high accuracy alignment I've more often found the low accuracy settings to provide worse alignment (more holes).  This could be a backup approach for when the high quality alignment fails, so will keep trying in the future.

@wishgranter great recommendations - using 40k key and 10k tie worked a charm:
https://www.dropbox.com/s/qm4urtq58sleovb/Screenshot%202015-09-15%2013.05.54.png?dl=0
https://www.dropbox.com/s/rw6az0a81ib70ho/Screenshot%202015-09-15%2013.06.07.png?dl=0
are these settings appropriate across all camera models / scenery types?

Thanks again guys



No  its  not proportionaly depending on scene and etc, its a  hard earned knowlege what to set to get best results...

contact me on muzeumhb@gmail.com so can explain it a bit more...
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