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Author Topic: DEM error but GCP RMS is very small  (Read 3953 times)

Phogi

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DEM error but GCP RMS is very small
« on: March 22, 2017, 10:43:32 AM »
Hi Alexey,

I met a similar issue as the thread showed before: http://www.agisoft.com/forum/index.php?topic=2151.15
But I tried both uncheck the geotags or set the GCPs to 0.001 etc., the DEM comes out will be varied to about 10 cm at some GCPs.

Could you give some suggestions of how can force the model to match with the GCPs better?

Thanks a lot.


Alexey Pasumansky

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Re: DEM error but GCP RMS is very small
« Reply #1 on: March 22, 2017, 10:46:53 AM »
Hello Phogi,

Which parameters you are optimizing for this project and which settings you are using to build DEM?
Best regards,
Alexey Pasumansky,
Agisoft LLC

Phogi

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Re: DEM error but GCP RMS is very small
« Reply #2 on: March 22, 2017, 02:51:30 PM »
Hello,

Thank you for your reply! The camera parameters I used are all the parameters in reoptimising, and in DEM generation I use dense point cloud and other parameters used default.

Thanks!

Alexey Pasumansky

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Re: DEM error but GCP RMS is very small
« Reply #3 on: March 23, 2017, 11:38:54 AM »
Hello Phogi,

Maybe you can provide the original image set and project file for us to check it in detail?
Best regards,
Alexey Pasumansky,
Agisoft LLC

Phogi

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Re: DEM error but GCP RMS is very small
« Reply #4 on: March 28, 2017, 12:34:04 PM »
Hi Alexery,

How can I give you the photos?

Chees,
Tim

Phogi

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Re: DEM error but GCP RMS is very small
« Reply #5 on: July 05, 2017, 07:38:42 AM »
Hi Alexey,

Sorry to raise this issue again, I recently met a dataset with RMS within 1 cm (Due to I set the marker accuracy as 0.002, otherwise the RMS have two points at 0.1m). So I forced the model with the GCPs, but the final result shows the elevations shifted at 0.4m or more for each GCPs. Is there possible be some reasons?

Thanks a lot!

Alexey Pasumansky

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Re: DEM error but GCP RMS is very small
« Reply #6 on: July 05, 2017, 01:28:42 PM »
Hello Phogi,

Do you mean that you are checking the elevation model value in the GCPs position? If so, please specify the reconstruction parameters used for the dense cloud and DEM generation.
Best regards,
Alexey Pasumansky,
Agisoft LLC

Phogi

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Re: DEM error but GCP RMS is very small
« Reply #7 on: July 09, 2017, 12:08:17 AM »
Hi Alexey,

In the alignment step I used default 40,000 points settings, and in the dense point cloud step I used medium quality, and for DEM I used Dense point cloud and enabled interpolation.

Would these parameters help?


Phogi

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Re: DEM error but GCP RMS is very small
« Reply #8 on: July 13, 2017, 08:49:37 AM »
Hi Alexey,

I got another dataset which is also wired, the photos flew along a road, and before importing GCPs the altitude error is about 2m, but after imported GCPs and reoptimise, the easting/northing/alt error all get at about 10cm at the GCPs and 11m at photo alt error. I checked the photo altitude should match the GCP elevation (before reoptimising).

I tried to set the marker accuracy to 0.001 and the RMS shows smaller at GCPs, but the estimated GCP elevation is much away to the actual GCP elevation.

Could you help to check what's wrong for the problem? I'm trying 1.3 and the photos are from DJI model FC6310.

Thank you.

Phogi

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Re: DEM error but GCP RMS is very small
« Reply #9 on: July 13, 2017, 09:08:13 AM »
Hello Alexey,

I mean in the GCP it has elevation of 94.366ft, and the alt error is 0.03ft, but the estimated elevation is 93.466ft, which is 0.1ft difference. How can I force the model to use GPC's height? I also noticed that the photos have slightly curvature at the edge of the flight area after optimising the cameras.

Thanks, 

Phogi

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Re: DEM error but GCP RMS is very small
« Reply #10 on: November 14, 2017, 08:01:14 AM »
Hi Alexey,

Continue with the similar phenomenon, I had some photos being adjusted the contrast due to they were too dark, then I processed them with other original photos together (I found the contrast function in PS can only work for one chunk, if merged the photos will lose the adjusted contrast). However, the adjusted photos had almost less than 1cm for all the GCPs' RMS in PS after reoptimised, but when the DEM was generated, the elevation differences compared to the GCPs can reach up to 0.4m.

Is this due to the adjusted photos? Except the contrast it shouldn't modified any other things. Also many GCPs are 0.001 m in RMS after reoptimised.

Could you give some hints?

Thanks a lot.