Decimate mesh bad import


#1

OK, here’s a mesh processing quirk I found when using R5:
I analyzed, fixed and decimated a mesh in R5 which was imported from a scan (Creaform VXelements).
Then I brought the mesh into David3D/HPScanFusion.
In David3D, the mesh had all kinds of holes in it all over the place.
Looked like someone sprayed a mist of acid on a whole cloth and the acid at through in little patches all over the place.
David didn’t do well in fixing that mesh imported from Rhino.
Can someone tell me what might cause this phenomena?
Thanx …


#2

have you got a little chunk of that mesh? messing around with meshes i had it happen that the normals of some polygons where inverted and seemed missing after using mesh repair tools.


#3

@cadman777, if you send or post the mesh or show a picture, it would help.

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c.


#4

Find attached an example of what I’m talking about.
2 files: 3dm & obj

SpeakerGrille1c3-mlc.zip (8.2 MB)


#5

Was the mesh fully welded and closed without naked edges or holes before the decimation ? If you run _Check in Rhino you’ll see whats all wrong with this mesh (apart from Rhino telling you “This is a good mesh”). :slight_smile:

I think the easiest way to fix such scans is to sample points and normals from the input mesh and create a new one. But this would give better results with the undecimated mesh.

I’ll attach and example: SpeakerGrille1c3-ml-1d_CG.zip (13.1 MB)

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c.


#6

Thanx Clement.

I ran the Mesh Repair Wizard till it was pretty good.
I tried to attach the file before doing any cleanup but it was too big.

I looked at your model and it looks pretty good.
Opened as an obj in David3D no probs (as exported from Rhino5).
I don’t mean to sound ignorant, but how would I go about doing this in Rhino?:
"… sample points and normals from the input mesh and create a new one."


#7

@cadman777, try CloudCompare.

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c.


#8

Yeah, I tried CC, but haven’t had time to learn it.
It’s simple, yet not so simple.
Has to do with not knowing how to process clouds correctly.
Everything in life has a method or a few methods, depending on the situation.
Simple means smart.
Complex means stupid.
It’s always that way … unless you’re talking law and government, in which case nothing makes any sense, confusion is reason, violence is peace, black is white, worthless is valuable, etc.
Is there any good introductory info (simple is better) that lays-out pointcloud processing steps in common sense terms that you can direct me to read?
It all comes down to knowing those steps when approaching pointclouds, and then knowing the software you’re using to do the job (and whether or not it has limitations).