Questions about the construction of ModelNet10-SO(3) dataset

[yd-yin]

Hi, thanks a lot for your great work and useful dataset!

Could you elaborate a bit more about the construction of the ModelNet10-SO(3) dataset? since I may want to reconstruct and re-render the images

For example, what are the intrinsic and extrinsic parameters of the camera? Is the original shape in ModelNet10 the reference "canonical" pose (i.e., identity rotation)?

Looking forward to your response Thanks!

[leoshine]

Hi,

Thanks for the interests of the dataset.

• Rendering setup You may choose any intrinsic matrix such that the rendered object fill up the image canvas (since we don't estimate intrinsic matrix). To do this, I recommend you to scale the 3D model to fit in a unit ball (diameter=1) before rendering. Here is a snippet of pseudo code :

  # centralize by AABB box center.
  minmax = vertices.minmax()
  min3d, max3d = minmax[:,0], minmax[:,1]
  vertices -= (max3d+min3d)/2                        # centralize by box center
  #
  _mags = np.sqrt(np.sum(vertices**2, axis=1))       # l2 norm of centralized vertices.
  scale = _mags.max() 
  vertices = (vertices / scale) * 0.5

For your convenience, one example of intrinsic matrix (OpenGL) based on above setup can be:

[[  5.8   0.    0.    0. ]
 [  0.    5.8   0.    0. ]
 [  0.    0.   -6.  -17.5]
 [  0.    0.   -1.    0. ]]

• Are all ModelNet10 in "canonical" pose? It has been a while, and I don't remember the details. As far as I can recall, I indeed manually corrected a few CAD models - but I not sure whether it was modelnet10 or modelnet40. You'd better double check it.

[yd-yin]

Hi, Thanks for your quick response and informative message!

I finally found that maybe it will be more convenient to render by myself:)

Thanks!

[yd-yin]

Well, sorry for the bother, but I got another problem...

I tried to render 3D models from ModelNet10 dataset by trimesh + pyrender, but just to find the renderings of some models are incorrect.

I'm not sure if it is caused by wrong face normals. Did you meet the same issue before?

Thanks a lot!

[leoshine]

Indeed. It can be the wrong surface normal or wrong winding of the three vertices of a face (if Trimesh generates the surface normal automatically). I ended up generating the surface from the triangle face definition myself, instead of using any surface normal defined in the CAD file. This at least corrects the back-facing problem, however, the rendered surface may not be that smooth.