Automatically fix mesh tunnels/holes

[AlexanderT]

Hi,

Sometimes in photogrammetry scanning, holes/tunnels appear on thin surfaces like on ears and cloth (please see image and model attached). Is it possible to detect them in Houdini automatically? Idea is to solve these issues on multiple scans running a few SOP's on a sequence of OBJ's.

Geomagic software can detect them as Small Tunnels and you can delete them there and cap the holes easily, so it is possible to define them mathematically although I can't find any tools in Houdini that can do the same.

Thank you!

mesh_tunnels_example.OBJ

[konstantin magnus]

There are greater chances of success by going one step back, eg. improving the meshing algorithm based on the underlying point cloud data.

Once you got hold of the point cloud, try (point replicate,) VDB from Particles, VDB reshape, VDB smooth and VDB convert to get a mesh thats closer to the real surface.

[AlexanderT]

Scans are processed in Reality Capture. There's no way of reprocessing the data. It will be great to find a way to detect/delete and cap those holes.

[flcc]

From my experience for this kind of shape, decrease the quality of one of the differents step, Alignement, meshing, or even reduce the photos size,
can result in better result, less noisy, and sometime less holes.
No warranty, just try. photogrametry is sometimes arbitrary, even esoteric.
The only guarantee of quality is the quality of the shots.
Improving this after, is not easy.

PS : Sorry, I didn't notice you weren't the guy who do the photgrametry process.

You can try meshMixer (free).
He's pretty good at plugging holes.

Edited October 11, 2019 by flcc

[konstantin magnus]

Hi Alexander,

 -> 

try this route:

• convert to VDB with VDB from polygons
• dilate with VDB reshape SDF
• close with VDB reshape SDF
• erode with VDB reshape SDF
• convert to polygons with convert VDB

Make sure to play around with all parameters and radii to get as close as possible.

fill_scan.hipnc

[AlexanderT]

Thank you Konstantin. VDB destroys a lot of detail and I need to preserve all mesh details and UV's. Ideally I just need to detect them, delete and then fill those those holes. Do you know any other way?

[konstantin magnus]

You could try to fill the missing pieces with inverted space carving (left) or by re-projecting depth maps (bottom) or rather their tracing curves (right).

 

 

[vinyvince]

On 10/13/2019 at 6:48 PM, konstantin magnus said:

You could try to fill the missing pieces with inverted space carving (left) or by re-projecting depth maps (bottom) or rather their tracing curves (right).

 

 

 

Looks very interesting but beyong my actual Houdini's confort zone, do you mind to share an example please?

 

Cheers

 

Vincent*

________________________________________________________________

Vincent Thomas   (VFX and Art since 1998)
Senior Env artist & Lighting & MattePainter & Creative Concepts
 http://fr.linkedin.com/in/vincentthomas

[StepbyStepVFX]

On 13/10/2019 at 12:38 AM, AlexanderT said:

Thank you Konstantin. VDB destroys a lot of detail and I need to preserve all mesh details and UV's. Ideally I just need to detect them, delete and then fill those those holes. Do you know any other way?

Just an idea, based on what Konstantin provided : once you have a closed mesh, maybe try to subtract the closed one from the original one, and then you will be left with the holes (inverted). Use these meshes to « tag » the borders of holes in the original mesh.

From there, reproject the detailed mesh onto the smooth/closed version of Konstantin, but only for the points that are not tagged. See what I mean ? By difference you can get the area of the holes, and use that to mask the reprojection process. Therefore you will have details everywhere except on the closed areas, that will be smooth.

But I won’t have time to propose you a file for that, I can just give you the idea :-)

[AlexanderT]

Hey guys, those are some really good ideas for sure. Thank you very much! 

konstantin will be good if you can provide a sample. That is very interesting indeed

StepbystepVFX thank you again, no problem, I will try to figure this out, that is a great idea.

[vinyvince]

On 16/10/2019 at 8:51 PM, StepbyStepVFX said:

Just an idea, based on what Konstantin provided : once you have a closed mesh, maybe try to subtract the closed one from the original one, and then you will be left with the holes (inverted). Use these meshes to « tag » the borders of holes in the original mesh.

From there, reproject the detailed mesh onto the smooth/closed version of Konstantin, but only for the points that are not tagged. See what I mean ? By difference you can get the area of the holes, and use that to mask the reprojection process. Therefore you will have details everywhere except on the closed areas, that will be smooth.

But I won’t have time to propose you a file for that, I can just give you the idea :-)

 

Edited August 21, 2020 by vinyvince