wrong estimate_point_cloud_normals

[l1346792580123]

🐛 Bugs / Unexpected behaviors

the results of estimate_point_cloud_normals are wrong.

Instructions To Reproduce the Issue:

I use the bunny obj from here. and the code is

import trimesh
import open3d
from pytorch3d.ops.points_normals import estimate_pointcloud_normals
from pytorch3d.structures.pointclouds import Pointclouds
mesh = trimesh.load('bunny.obj', process=False, maintain_order=True)
points,face_idx = trimesh.sample.sample_surface_even(mesh, 40960)
np.savetxt('tmp.xyz', points)

pcd = open3d.io.read_point_cloud('tmp.xyz')
pcd.estimate_normals()
normals1 = np.asarray(pcd.normals)

points2 = torch.from_numpy(points.astype(np.float32)).unsqueeze(0).cuda()
pointclouds = Pointclouds(points2)
normals2 = estimate_pointcloud_normals(pointclouds, 10)
normals2 = normals2.squeeze().detach().cpu().numpy()

normals1 = (normals1+1) / 2
normals2 = (normals2+1) / 2

np.savetxt('a.txt', np.concatenate([points,normals1],axis=1))
np.savetxt('b.txt', np.concatenate([points,normals2],axis=1))

The visual results of open3d and pytorch3d are as followed.

[bottler]

Both the images look a little surprising: The upper one varies less than I'd expect, and the lower varies more than I'd expect, assuming you are mapping the normal to color space. Can you investigate the plotting, and perhaps plot the normals as arrows? And what happens when you vary the neighborhood_size and set disambiguate_directions=False?

[l1346792580123]

The arrow results of open3d and neighborhood_size=10,30,50, disambiguate_directions=True, are shown below

and the result of neighborhood_size=50,disambiguate_direction=False is shown below

[l1346792580123]

I found the wrong normal vectors come from the wrong output of symeig3x3. When I set use_symeig_workaround=False the results are normal.

Moreover, I found that the normal vectors are more consistency when setting disambiguate_directions=False, which is the opposite of what the parameter originally intended. The results of disambiguate_directions=False,use_symeig_workaround=False and disambiguate_directions=True,use_symeig_workaround=False are shown below