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Author Topic: Shift in ortho image during export  (Read 3188 times)

Davier

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Shift in ortho image during export
« on: April 26, 2019, 07:13:22 AM »
I have been building orthophotography from historical imagery now for nearly five years and am having a real struggle lately with the accuracy of the exported orthos.

When orthos have been built, I check the location of the control on those orthos prior to export. Once exported, I overlay the control on the orthos again in Global Mapper. I am finding that during the export process, the orthos are shifting meaning that the control does not now fit and the orthos have moved out of position. This is random and not by the same amount each time.

I have built these orthos a number of times to try and get a better result, each time taking nearly three days to process them so I am losing valuable time.

Can you please suggest why there is a shift error.

Alexey Pasumansky

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Re: Shift in ortho image during export
« Reply #1 on: April 26, 2019, 01:42:22 PM »
Hello Davier,

Are you using scanned images with the fiducial marks?

How many control points are used to the projects typically, what is their distribution across the area of interest and how large is the error that you are observing?
Best regards,
Alexey Pasumansky,
Agisoft LLC

PROBERT1968

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Re: Shift in ortho image during export
« Reply #2 on: April 27, 2019, 06:07:17 AM »
Davier,

I don't think so that it is any bug but from what I am seeing is that the historical aerial photos does not have their known coordinates in the old days...

What I would do is place each the markers  using the x,y,z first and then when you are done with it hit the Update button.

Review them and then do the workflows and export them to orthomosaic and see what was the results

Davier

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Re: Shift in ortho image during export
« Reply #3 on: April 29, 2019, 02:47:37 AM »
Hi Alexey,

Yes I am using scanned images with fiducials. No issues there. The project that I am currently working on has 275 frames and I have used 62 control points which are distributed evenly throughout the project area.

As far as errors are concerned, they are random being from less than 1m through to 11m in some areas. 

I am currently reprocessing the whole project, putting in a lot more control first to get the setup as tight as possible. Hopefully that will give me a good result but I am not holding out too much hope.

Alexey Pasumansky

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Re: Shift in ortho image during export
« Reply #4 on: April 29, 2019, 02:12:59 PM »
Hello Davier,

Are all XYZ coordinates for the control points known with high accuracy?

Have you tried to leave some of the markers unchecked to validate the accuracy according to their errors, are you observing large errors for them  in such case in the Reference pane?
Best regards,
Alexey Pasumansky,
Agisoft LLC

Davier

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Re: Shift in ortho image during export
« Reply #5 on: May 01, 2019, 05:44:37 AM »
Hi Alexey,

The imagery is flown with a wide angle camera (11.5cm lens on a 18 x 18cm format) at 25,000 feet so the raw GSD is about 0.94m. The control is accurate to +/-2m in XY but to about 0.2m in Z.

What is happening is that I am getting a reasonably good set up (Alignment / AT) and even right through the process, getting errors in the +/-4 - 5m range which I am expecting. When I check the orthos in Agisoft after the build, with the control positions overlaid, they are all quite reasonable and expected given the GSD and the control accuracy. When I export the orthos from Agisoft however, the orthos shift their position which I have never seen before. That is my problem!!

The attached files show two different points at opposite ends of the project. The "Agisoft" files show where the control point falls when the control is viewed within Metashape itself. The "Global_Mapper" files are where the exact same control file is viewed over the exported orthos when loaded into Global Mapper. The images have shifted. Why?

Davier

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Re: Shift in ortho image during export
« Reply #6 on: May 08, 2019, 05:48:59 AM »
Does anyone have anything further on this? The silence is deafening.

harrytwomey

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Re: Shift in ortho image during export
« Reply #7 on: May 27, 2019, 03:03:22 PM »
Does anyone have anything further on this? The silence is deafening.

As i a newbee here, this might not be an answer but have you checked that the export coordinate system is identacal to the one used to generation, that tha datumare the same

Alexey Pasumansky

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Re: Shift in ortho image during export
« Reply #8 on: May 28, 2019, 07:01:42 PM »
Hello Davier,

Can you share the project file in PSZ format with the alignment results only and placed markers to support@agisoft.com?
Best regards,
Alexey Pasumansky,
Agisoft LLC

Rockflower

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Re: Shift in ortho image during export
« Reply #9 on: March 24, 2020, 04:02:19 AM »
Is there any solution for this problem?

I am also having the same problem. Ortho images in Metashage have good alignments with GCPs, but once I exported to TIF, they shift randomly by half to a meter.
The coordinate system I am working on is NAD83 State Plane for Metashape file and GCPs. The location file of photos is in WGS83.
Export Orthomosaic function in WGS83 and NAD83 State Plane give different results.