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Author Topic: DEM Mismatch/Slope  (Read 3796 times)

Toby

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DEM Mismatch/Slope
« on: October 11, 2013, 11:19:01 AM »
Hi,

I produced a DEM in Photoscan yesterday. I've tried to validate the results by comparing height derived from photogrammtery in Photoscan to spot heights from a ground survey. The differences between the two seem to show a systematic error where one side of the DEM is lower than the independently surveyed points, whereas the other appears higher than the surveyed points (e.g. the entire DEM is sloping in a uniform direction).

Has anyone encountered this issue or have any insight into what might be causing it?

Any help would be great,

Thanks.
« Last Edit: October 14, 2013, 11:33:44 AM by Toby »

Alexey Pasumansky

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Re: DEM Mismatch/Slope
« Reply #1 on: October 11, 2013, 06:17:14 PM »
Hello Toby,

We recommend to use optimization based only on ground control points (with 1-5mm Marker Accuract parameter used) to remove non-linear distortions of the sparse point cloud.
Best regards,
Alexey Pasumansky,
Agisoft LLC

Toby

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Re: DEM Mismatch/Slope
« Reply #2 on: October 15, 2013, 12:52:24 PM »
Hi Alexey,

Thank you for your assistence. The point cloud has been linked with circa 20 points for ground control using the parameters you suggested - the problem still remains. I've also tried the who process again, without processing in chunks and I still seem to get the systematic mismatch (one side higher, one lower) between the DEM and the ~6000 points I'm using to check the height errors.

Perhaps it is an issue with the ground survey data?

Alexey Pasumansky

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Re: DEM Mismatch/Slope
« Reply #3 on: October 15, 2013, 04:16:42 PM »
Hello Toby,

Could you provide the project file for our internal checks?
Best regards,
Alexey Pasumansky,
Agisoft LLC

Toby

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Re: DEM Mismatch/Slope
« Reply #4 on: October 16, 2013, 11:26:31 AM »
Hi Alexey,

That would be great - I've PM'd you a download link.

Cheers, Toby