3D Print: Non Manifold faces. Best practice?

[albertkiefer]

Hi,

I am using Photoscan to reconstruct archaeological sites. I then have to process data to make a 3D printable surface.
However Photoscan often produces non-manifold planes in the geometry. And also many times the normals are flipped randomly so that it is hard to create a thickness that is necessary for making a watertight 3D printable surface.

What is best practice?

[Wishgranter]

few options ( but keep in mind that this problem exist with every scaning solution - laser, structured,photogrammetry ):

1. in PS 1.0.0 go to TOOLS - MESH - VIEW MESH STATISCTICS = FIX ERRORS, as i have discussed this part with agisoft it clean mesh for most errors, but its will be never perfect....

2. REPAIR in external app, like GEOMAGIC, XOR and etc. it better but still not perfect too :-)) sometimes it must repair 2-3 times before its good.

3. RETOPOLOGY in externall app( Zbrush, Mudbox, 3DS MAX, 3D COAT - automatic mode ) its best way but sometimes complicated, its about creating clean new mesh from the original scann data. http://www.youtube.com/watch?v=qKTUIsPQ_uM

4. Printing solution - most of the 3D printer sw should be capable of repairing mesh ( STL repair ) at least Z-Corp have this option....

[albertkiefer]

Problem with 3rd party printing is to get past their 'firewall' of model checks. Usually if non-manifolds are in the model it gets rejected. Even if they have software to fix it.

I run a decimation pass on the high-res model in PS and usually that is when errors start to occur...

Albert

[chrisd]

netfabb Basic is free, and can repair a lot of these issues, but its 32 bit only.

netfabb also has a cloud service which is free (or was free) that can handle more repairs, but you have to upload/download your model which can be a hassle.

I purchase netfabb Pro which is 64 bit, and has thickening and boolean functions.

[albertkiefer]

CHRISD,

Wouldn't I lose the image information? I print to a colored material to retain some of the landscaping and archaeological details?

Albert

I attach an image for your information :-) It's a composite render of the 3D reconstructed walls and some 3D modeled geometry to extend where the walls used to be.

Albert

[chrisd]

Albert,

Typically you would lose the color info, unless your repair application can preserve vertex color.

There is a process in Meshlab to reproject the vertex color from one mesh onto another, so in theory, you could repair the mesh in another app (I have found Meshlab not very useful for repair), bring it back into Meshlab and transfer the color from the bad mesh to the repaired mesh.

I have yet to try this myself.

[Wishgranter]

mostly the color printing is done with help of textures ( vertex is OK, but with lower details )  ......

[albertkiefer]

True,

I use the image maps. That's the problem when bringing models to external applications for repairs.
Also I work on Mac and Meshlab even crashes when I try to open a file (even very small ones!). So it's not a viable solution.

I have strated to look at Topogun but rebuilding a complex (I need the broken off walls in the reconstruction) model in Topogun would take too much time.

It seems that PS has some issues with large more or less regular shapes (the brick walls). It throws in some big chunks of noise in an otherwise very regular wall.

But the most pressing problem is self intersecting geometry...

[Wishgranter]

as im mentione the mesh problems are common to all "scaning" technologies. some can eliminate it ( not all ) some not. try the 3D COAT and its AUTORETOPO tech, even the app cost reasonable price.... if need assistance let me know....

[Alexey Pasumansky]

Hello Albert,

What reconstruction mode are you using Sharp or Smooth?
In Smooth there should not be such effects that you are describing.

[albertkiefer]

I have just seen the result of the same data reconstructed in version 1.0 and it is STUNNING! Much less noise and very much closer to the situation on location!! I am very excited.

I will gradually decimate a high poly mesh now back down to something like 75000 polygons. From that Mesh I can take it into any 3rd party software and add a thickness so that I can make a 3d print.

It it advisable to decimated in one step from, for example, 11 million polygons down to 75000? Or is gradual 'down sampling' better to retain original shape?

[chrisd]

I use the image maps. That's the problem when bringing models to external applications for repairs.
Also I work on Mac and Meshlab even crashes when I try to open a file (even very small ones!). So it's not a viable solution.

OK, so you mean the UVs get get removed, yes that is the other problem.

Sorry Meshlab does not work for you.

Blender might work?

[albertkiefer]

Chrisd,

might be but for the time being I need to concentrate on solving within existing workflow because of time constraints. And bringing over super heavy models may ontroduce big problems for some 3D apps...