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Author Topic: DEMs constantly sloping up from one side?  (Read 1062 times)

kfish

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DEMs constantly sloping up from one side?
« on: July 25, 2023, 05:34:18 AM »
I've been trying to create DEMs of some small scale topography but I seem to be constantly getting issues where the DEM is showing a strong slope from one side of the model to the other. Attached DEMs of two examples of this. I've been following the process laid out in:

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/2041-210X.13476

Bayley, Daniel TI, and Andrew OM Mogg. "A protocol for the largeā€scale analysis of reefs using Structure from Motion photogrammetry." Methods in Ecology and Evolution 11.11 (2020): 1410-1420.

It seems to work fine through all the steps but the resulting DEM has this weird slope issue which is preventing me from extracting information about the local features. Any ideas?

Alexey Pasumansky

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Re: DEMs constantly sloping up from one side?
« Reply #1 on: July 25, 2023, 03:35:17 PM »
Hello kfish,

How you are performing georeferencing in this project? Are you basing on camera or marker coordinates? If markers are using, can you provide the screenshot of ortho/DEM view where all the placed markers are visible?
Best regards,
Alexey Pasumansky,
Agisoft LLC

kfish

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Re: DEMs constantly sloping up from one side?
« Reply #2 on: July 25, 2023, 10:51:05 PM »
Hi Alexey,

I am using the scale bar that is visible in the images to place markers and then create scale bars with known lengths in Agisoft from that. The DEM is then being constructed based on those scale bars. For example, see the attached picture below (one without the markers and another test on a different spot with the markers on it). Right now i only have scale bars in one section of the image, could this be causing issues? Is there a better workflow to follow for using scale bars to generate DEMs?



Thanks

Alexey Pasumansky

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Re: DEMs constantly sloping up from one side?
« Reply #3 on: July 26, 2023, 04:06:26 PM »
Hello kfish,

Scale bar distances are only used to apply proper dimensions to the model. And as for the model orientation in space you need either to use the known coordinates of cameras and/or markers (such instances should be checked on in the Reference pane) or apply the rotation manually using Rotate Object tool, but the latter option is surely less accurate.
Best regards,
Alexey Pasumansky,
Agisoft LLC