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Author Topic: DEM from Mesh not dense cloud  (Read 1484 times)

jbueno6

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DEM from Mesh not dense cloud
« on: August 07, 2018, 05:49:40 PM »
Hello all,

I currently have a project creating DEMs. We use GCPs out in the field and we use an RTK-GPS system to get elevation with accuracy of 5cm. we use about 10-15 GCPs for about 300 meter length site. My current workflow for creating the DEM is :
-placing the GCPs
-creating the dense point cloud
-classifying ground points (high vegetation at this site, we dont care about the vegetation)
-building the mesh BASED off the classification
-clean out some geometry/vegetation
-build the DEM from the MESH not the dense cloud
When I was building the DEMs from the dense cloud it was bringing in all the vegetation which we do not need even if I use the ground point classification?
The tutorial states:
"Digital elevation model can be generated based on the dense cloud or mesh model. Usually first
option is preferred, as it provides more accurate results"
How much more accurate is the dense cloud compared to the mesh?

Thank you!

stihl

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Re: DEM from Mesh not dense cloud
« Reply #1 on: August 08, 2018, 01:22:03 PM »
Any alterations made by Photoscan when generating the mesh from the dense cloud will bring these changes to the derived DEM from the mesh as well. Therefor it's prefered to do it straight from the dense cloud.
However your approach by manually cleaning some geometry and or vegetation from the mesh and then using this as a basis for the DEM is not a bad approach as you have a bit more control over how your DEM (DTM in this case) will look like.

When generating the DEM you can select which point classifications it should use during interpolation. When you've classified your points through auto classification or manual you can use this classification. You can set this up in the Build DEM window when pressing on the select button at 'Point classes'.