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Point Cloud has piles of pixels on a flat road that create erratic cross sections?

Hello,
I have flown a concrete street in town and processed it. My drafting software is creating some erratic cross sections on what should be a smooth road with curb and gutter. I zoom in close to look at the densified point cloud and it appears that there are piles of pixels in the middle of the road? Obviously this is relating to the erratic cross sections. What can I do to improve this? Also the face of the curb and gutter tends to be smoothed out and not abrupt as I would like it. I have tried several settings in Pix4D including medium and sharp setting in DSM/Mosaic. The point cloud settings are Image Scale = 1/2; Point Density = Optimal; Min # of matches = 5; using both filters on. Any help would be greatly appreciated.
Thanks,
Hanns.

It sounds like you need to make MTP’s, surfaces, GCP’s, etc. They will help the images “smooth out” and get rid of some of the noise (piles of points). In order to have an abrubt surface on the curb you will have to have some oblique images in your project as well as nadir, just like a building facad. That would be where I would start. Hope it helps.

I am getting this too would be good to know the best ways and software to filter out the noise

I agree with Whitnie, you can always add GCPs, manual tie points and if needed remove points.

You can as well clean the point cloud with external software and then import the point cloud and process step 3 with the imported, but in general is not needed.

And if you want a nice DSM/mosaic, then you can add surfaces in the raycloud, that will help for dsm and orthomosaic, and additionally, edit the mosaic with the mosaic editor.

Any luck Hanns?

I am currently doing a large-ish linear urban project (approx 9km long with atleast 3 times that in roads) flown by a client and getting the same result on my roads (mix of chip seal and bitumen). I am using similar settings to you as well (i am using min# =6). It is worse in areas of shadow but not all shadows. It is difficult to determine a reason other than false / poor feature matches on the road.

MTPs is not an option for me as it would require such a large number of them and the time to implement them would be longer than practical. Will lowering the scale help with the point cloud by generalising features at the expense of accuracy?

Thank You all for your advice! I flew an area at a lower altitude and increased my photo overlap to 85% front and 75% side overlap. This really seamed to help. I also added some obliques as Whitnie suggested. Thank you. I generally think that it was the way I initially collected the data. Josh what is the external software that you use? Josh when I add a surface in the raycloud, are you suggesting that I surface say the concrete pads and curbs? To be clear on this “Surface” idea, first I need the initial point cloud densification correct? Then add these surfaces in the raycloud and then reprocess the point cloud and Mosaic? Gareth, I’m not sure that will help. I would like to get the DSM in better shape though so I can use it to create contours in Microstation.
Thanks, Hanns.

1 Like

Hanns, Did you ever find a solution? I am having the same problems with piles of points on a flat road and I am unable to contour my projects in AutoCad. Thanks

 

Tom

@Hanns: Regarding the surfaces, I believe that Josh meant something similar to what is described in this article: 
https://support.pix4d.com/hc/en-us/articles/202560449 . The idea is to add a surface on the road, or the sidewalk once the densified point cloud is created (after step 2) and then check " Use for DSM and Triangle Mesh" in the surface options in the right hand panel. Then, you can run step 3 and the DSM should be flat (i.e. without noise) in the areas with surfaces.

@Josh: I’d also be curious to know about the external software you use to clean the point cloud. 

@Tom: Please check the previous comments on the post as well as Hanns’ last comment. These should give you hints as to how you can proceed to remove the noise in your project.

Some good suggestions in here. I have struck this issue many times in the past myself, and have not been able to resolve it fully. While adding a surface works well for car parks, roads are not flat.  They have a rounded peak to assist water run-off.  Hence putting a surface will flatten the road, would it not?

 

Roads generally lack features to match using photogrammetry.

 

LiDAR is the most viable option, once the price of airborne (UAV) sensors drops - which it soon will, thanks to the race for Autonomous Vehicles.  In the meantime, we minimise point cloud noise and manually edit when needed.