From Photoscan to Shapeways: Process 2/N

TL;DR:  Nice idea, but fail.

Holy crunch this is taking a lot of hands on stuff figuring out what works, and what doesn’t.   I decided to step back and take a look at the strength / weaknesses of everybody and see if I could meta a process out of it.

Program Strengths Weaknesses
Agisoft Photoscan Can fill holes; gets normals correct when filling holes
Can Export and Import .OBJ
Can Export and Import WRL
Unique: can create textures from images
Cannot select only visible surfaces for deletion; has to select hidden as well
Can only close holes; does not always generate manifold
Cannot export STL
Cannot resize
Import object cannot have been moved
Netfabb Great job filling holes
Can detect non manifold
Unique: Very good at making things manifold automatically
Import/Export OBJ, STL, WRL
Can resize
No direct mesh manipulation
Free version cannot remove extra shells
Blender Unique: Can do union operations to add missing chunks together
Can detect non-manifold very well
In depth mesh editing
Can resize
Thin wall detection
Import/Export OBJ, STL, WRL
Can remove extra shells
Fills holes with akward normals
Cannot auto-fix manifold
Deleteing faces causes complex manifold problems which escalate quickly
Windows / etc Can ZIP files heh
Shapeways Import texture with ZIP files
Thin wall detection
Unique: Can print in color!
Cannot directly import multi part objects unless ZIP first
Cannot resize
Thin wall fixes loose texture
Cannot get texture when importing OBJ

Proposed Flow

  • Generate mesh
  • Save as A.obj
  • Use circle and block delete to remove chunks to be replaced in blender
  • Save as B.obj
  • Import B.obj
  • Fill holes / clean up / repair
  • Save C.obj
  • Import A.obj
  • Import C.obj – should be manifold
  • Create additional surfaces D1,D2 etc to union using A for reference
  • Union them with C <– not sure if this will work every time. 
  • If it works, save as F.obj
  • If unioning does not work, then:
    • Import B.obj
    • Prune surfaces D1,D2 etc so that there is no overlap with B
    • Create faces to join B and D1,D2 etc so that a fill holes will do the right thing
    • Save as E.obj
Agisoft (if stuck at E)
  • Load E.obj
  • Fill holes
  • Call this F.obj
  • Load model from F.obj
  • Generate textures
  • Export as G + GT (.obj)
  • Start over
  • Load G + GT (.obj)
  • Relocate, Orient
  • Scale, Apply scale
  • Thin wall detect
  • Save as H  + GT (.X3D)
  • Zip H+GT to HZ
  • Upload HZ
  • Look at thin walls situation -> leave open
  • Fix thin wall situations (and other problems)
  • Save as I + GT (.x3d)
  • Zip I+GT to IZ
  • Replace with IZ
  • Hopefully can print.

Wow, that’s a lot of steps.   No wonder I’m a bit frustrated.  

Update as of 6/1 (3-4 days after writing this): 

I tried it.  Twice.   5 hours later: It’s a fail.     The reason is that:  When I get to step G->H in Blender – when I do any fixes in blender – if those fixes involve cutting away dead faces and closing holes or anything like that – I loose texture.  As I usually have to do this surgery around places where I filled it in during step C+DN, Its all over the model, and It would look ugly.

However, I did learn a bit about fitting NURBS spheres onto human faces.   You go into Alt-Q 4-way view (Top, right, front), and first fit the edge pieces (where the surface comes all the way out to the control point); before going on to the other bits.  In the case of a human head, the anchor points are:  just above the ears, an imaginary line going back from the chin, just under the nose, etc.    This could be its own blog post, but I’d need more practice to verify that it works well every time. 

Next up I’m going to try a much-reduced polygon count – get rid of some of this detail that causes the thin walls.  The idea would be to use color and texture to make it look like the human.

Author: sunnywiz


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