Volume Difference Between Point Clouds

Good morning:
I have laser-scanned point clouds of a passenger car before and after a collision that crushed the roof. I would like to calculate the volume of the undamaged vehicle (ignoring the ground clearance beneath the body created by the tires). I would also like to calculate the volume of the wrecked vehicle to determine the volume reduction in the collision.
Can you make any suggestions on how I could go about turning the point cloud into a closed solid (with a relatively complex shape that reasonably approximates the crushed region) so I can have Rhino separately calculate the interior volume of the two models?

Hi Don - it might be worth a try to test the V8/WIP’s ShrinkWrap tool - it can take point clouds as input.


Hi Pascal:
Thanks for the reply. The name ShrinkWrap sound perfect but I have no Idea how to get started. How do I find the tool?

Hi Don -

You’ll need a recent Rhino 8 WIP and run the ShrinkWrap command.

Thank you! I didn’t even realize the WIP was available to me. I’m downloading it now and I can’t wait to try it. I’ll put my results summary in the forum when I’m done.

@doncstevens you may find the new v8 WIP ReducePointCloud command helpful as well for this task.

Hey @wim,
Great to hear that the ShrinkWrap feature is available for testing already! I’ve been waiting for it for quite some time now.

When was it added to the WIP? I’ve been following the release notes but couldn’t find any mention of it.

Hi Mariusz -

On Windows, it’s only been in there for 2 or 3 weeks. YouTrack issues have mostly been invisible to the public until a few days ago. A full announcement of the feature is still pending a severe crash issue, but, as I understand it, can come any day now.

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Hi Pascal.
I’ve been experimenting with the shrinkwrap and it’s really neat. I cleaned up my point cloud and worked with the settings to get the mesh to fit tightly around it.
I can’t find information in the help file about how the settings of the shrinkwrap command change the result, so I’ve just been experimenting. Can you give me any information on what Inflate, Offset, and the other setting do? How large can the holes that it fills in the PC be?
What I’m struggling with is that the mesh I get back is not a single polygon thick (so I can close it and compute the volume). The shrinkwrap covers the outside AND inside and makes a thick shell around the point cloud surface.
What do I need to do to make the doors shrinkwrap only cover the outside of the car?

How was the car scanned ? … do you have separate scans for inside and outside?

If Rhino doesn’t work you can use “CloudCompare”, it is free.
Use the Plugins / Poisson Recon function to create a closed watertight mesh from the pointcloud.
Then (Edit > Mesh > Measure volume)

I just tried the ReducePointCloud and Shrinkwrap tools… Very Nice !! Well done !!
Will Version 8 have any other new Pointcloud tools ?