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Author Topic: Accuracy (round N)  (Read 20128 times)

George

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Accuracy (round N)
« on: December 20, 2012, 12:12:15 PM »
Hi all who concerned with aerial photography
what do you think would be the precision of the resulting DEM and Mosaic (XYZ) if the GCP arranged at the PS are of the following errors?
Btw, could continious optimization of the point cloud help?
Another question is would it help if I push down the error (in meters and pix) to a 0.0xxx values? Could it in the end spoil DEM?
Cheers
« Last Edit: December 20, 2012, 02:04:31 PM by George »

Oli63

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Re: Accuracy (round N)
« Reply #1 on: December 20, 2012, 01:55:23 PM »
Don't know where is the problem. The results look fine, partly even incredibly good. The 3 spikes might have to to with bad overlapping or any other reasons, but not really a problem.
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George

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Re: Accuracy (round N)
« Reply #2 on: December 20, 2012, 02:42:27 PM »
... there is no actual problem with that ... I also think that the accuracy displayed is quite good and it appeared from the first try. But this is just at Photoscan GCP window.

The actual problem is that the final result systematically does not match DTM (the official one). The delta is around +- 0,6-0,7 at different places of the model, which seems to be quite weird considering accuracy of GCPs.

Below some examples of XY and XYZ tests (see images names) plus random samples - intersection lines.

Yeah ... one short comment is that the accuracy of XY to a degree dependent on my fingers - just clicking mouse button at ArcGIS
« Last Edit: December 20, 2012, 02:44:27 PM by George »

George

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Re: Accuracy (round N)
« Reply #3 on: December 20, 2012, 02:43:10 PM »
...

George

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Re: Accuracy (round N)
« Reply #4 on: December 20, 2012, 02:45:38 PM »
...

Alexey Pasumansky

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Re: Accuracy (round N)
« Reply #5 on: December 20, 2012, 02:51:16 PM »
Hello George,

Do you have a scheme of the GCP positions on the reconstructed area?
Best regards,
Alexey Pasumansky,
Agisoft LLC

George

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Re: Accuracy (round N)
« Reply #6 on: December 20, 2012, 03:07:39 PM »
Hi Alex,
please attached. The area is relatively large - approx. 200 ha
May be you could recommend something to that?
Cheers, George

George

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Re: Accuracy (round N)
« Reply #7 on: December 20, 2012, 03:19:57 PM »
In addition the workflow was the following:
1. Alignment based on camera positions. Quality - medium (unfortunately) since High didn't work at a part of the imagery
2. Gradual selection (reprojection error  around 3)
3. Import of GCP and their arrangement at the imagery (a circle of arrangements in order to reduce an error)
4. Optimization of the point cloud. At that stage error became low - somewhat at the level 0.xxx
5. Another round of GCPs adjustment - error became extremely low 0.0xxx
6. Geometry and the rest stuff
7. GIS analysis (XYZ tests and Z samples)
« Last Edit: December 20, 2012, 03:30:02 PM by George »

George

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Re: Accuracy (round N)
« Reply #8 on: December 20, 2012, 04:07:54 PM »
just in addition ... I would have appreciated if the error between DEM and DTM would had been fairly regular (+- 0.0x or even 0.00x) but it is irregular and jumps in a range of +- 1.xx meters which doesn't make confident in the model in general. Whereas individual parts may be fine

fpbv

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Re: Accuracy (round N)
« Reply #9 on: December 20, 2012, 04:17:50 PM »
George

Which camera are you using?

Is it a full frame camera?

Alexey Pasumansky

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Re: Accuracy (round N)
« Reply #10 on: December 20, 2012, 04:39:58 PM »
Hello George,

Seems like the "bowl-effect" is not completely removed during optimization.
Even with unused 4 and 5 points the positions or GCPs are OK (however, it would be better to use more points n the center and on the bottom).

Could you please check the markers with large errors - seems like these are: 10, 11, 8, 9.
After that we recommend to optimize the alignment with marker accuracy set to zero.
Best regards,
Alexey Pasumansky,
Agisoft LLC

George

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Re: Accuracy (round N)
« Reply #11 on: December 20, 2012, 04:45:48 PM »
Lumix LX5 - very simple stuff tho :)

but 24 mm angle, which is quite good

George

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Re: Accuracy (round N)
« Reply #12 on: December 20, 2012, 04:53:41 PM »
Alexey,
could you explain please "bowl-effect". It stands for ...?
Will try to place more points in the center. Tho it is not an easy task. Since there are no clear objects exactly at that place of the site.
Do you mean Markers accuracy at Ground Control Settings?

George

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Re: Accuracy (round N)
« Reply #13 on: December 20, 2012, 04:56:03 PM »
Alexey, what do you think about the workflow? Generally it is default but when it comes to Gradual Selection etc. is it reasonable? Several rounds of optimization?
« Last Edit: December 20, 2012, 05:06:09 PM by George »

Alexey Pasumansky

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Re: Accuracy (round N)
« Reply #14 on: December 20, 2012, 06:02:32 PM »
Hello George,

Under "bowl-effect" I mean obvious and usually huge model distortion, like on the attached image.

The workflow described is fine.
Removing outliers and points with large reprojection error for optimization is required for most cases. Repeating such procedure two or three times may improve the results.
Best regards,
Alexey Pasumansky,
Agisoft LLC