Anomalous points below ground surface

[amwade]

I've been running into a problem with random anomalous points in my dense point cloud. The point cloud is derived from images shot using a UAV. Looking from above the point cloud it looks great. But when you flip the point cloud and look below the ground surface there are numerous points aligned way below the surface. The point cloud is roughly 82 million points and I'm guessing there are 10s if not 100s of thousands of points below the ground surface. Not a big deal for the surface model, but when I run a ground classification these get included and make a really odd looking digital terrain model. The model ends up with big spikes dipping below the ground surface.

Has anyone else had this issue? Short of going through and erasing all of these is there a way to remove or avoid the problem?

[toffersan]

Hi! I had same problems with my clouds. What i tried, was exporting these clouds to cloud compare (free software
). There you can run some noise filter under : Tools-> Clean.  After getting a hopefully cleaner dense cloud, i was creating a mesh in cloudcompare and then reimporting this mesh to agisoft for DEM generation, because Agisoft is not able to import dense clouds.
Maybe this helps!
Greetings toffersan

[amwade]

Thanks Toffersan! I've worked with cloud compare before and will give the noise filter a shot. Is there any specific parameters you'd recommend?

[toffersan]

I just started this week to clean my clouds with CC, so putting the parameters is always an experiment for me! But it helped also to repeat with  the same filter SOR filter for example, again and again!

[Alexey Pasumansky]

Hello amwade,

You can also try to run the ground points classification procedure and then exclude "Low points (noise)" class from the DEM generation procedure.

[amwade]

Thanks Alexey, I'll give that shot

[amwade]

Thanks again Alexey that did the trick. There are still a couple of noise points that didn't get classified, but overall the DTM looks a lot better!