How to assign a quality value to each vertex in a mesh?

[ghost]

Hello,

I have numpy arrays of vertices, faces, and vertex normals that I can use to define a mesh with pymeshlab.Mesh(). I also have an array of scalar values corresponding to the vertices. Based on my reading, it seems like I want that array to be the vertex_quality_matrix of my mesh. Unfortunately, I can't figure out how to set that. I even looked around Meshlab but didn't see a way to assign quality to a mesh there either. I am very new to Meshlab so I am likely not understanding something.

Here is an example of what I am trying to do with a small cube in an interactive Python session:

>>> import pymeshlab as pyml
>>> import numpy as np

>>> verts = np.array([
       [-0.5, -0.5, -0.5],
       [ 0.5, -0.5, -0.5],
       [-0.5,  0.5, -0.5],
       [ 0.5,  0.5, -0.5],
       [-0.5, -0.5,  0.5],
       [ 0.5, -0.5,  0.5],
       [-0.5,  0.5,  0.5],
       [ 0.5,  0.5,  0.5]])

>>> faces = np.array([
       [-0.5, -0.5, -0.5],
       [ 0.5, -0.5, -0.5],
       [-0.5,  0.5, -0.5],
       [ 0.5,  0.5, -0.5],
       [-0.5, -0.5,  0.5],
       [ 0.5, -0.5,  0.5],
       [-0.5,  0.5,  0.5],
       [ 0.5,  0.5,  0.5]])

>>> vnorms = np.array([
       [-0.57735027, -0.57735027, -0.57735027],
       [ 0.33333333, -0.66666667, -0.66666667],
       [-0.66666667,  0.33333333, -0.66666667],
       [ 0.66666667,  0.66666667, -0.33333333],
       [-0.66666667, -0.66666667,  0.33333333],
       [ 0.66666667, -0.33333333,  0.66666667],
       [-0.33333333,  0.66666667,  0.66666667],
       [ 0.57735027,  0.57735027,  0.57735027]])

# arbitrary values to go with vertices
>>> vals = np.array([0.84328472, 0.69231293, 0.13644346, 0.33825513, 0.30680527,
       0.72530452, 0.15571249, 0.92643005])

With those arrays, I can create a pymeshlab.Mesh object like this:

>>> box = pyml.Mesh(vertex_matrix=verts, face_matrix=faces, v_normals_matrix=vnorms)

From that I can read back out the vertices, faces, and vertex normals I set. The vertex quality matrix is also initialized:

>>> box.vertex_quality_matix()
array([0., 0., 0., 0., 0., 0., 0., 0.], dtype=float32)

However if I try to set them to my desired value, I get an AttributeError:

>>> box.vertex_quality_matrix = vals
...
----> 1 box.vertex_quality_matrix = vals

AttributeError: 'pymeshlab.pmeshlab.Mesh' object attribute 'vertex_quality_matrix' is read-only

If I try to instantiate a new mesh with vertex_quality_matrix as a parameter, I get a TypeError with the constructor:

>>> box2 = pyml.Mesh(vertex_matrix=verts, face_matrix=faces, v_normals_matrix=vnorms, vertex_quality_matrix=vals)
...
----> 1 box2 = pyml.Mesh(vertex_matrix=verts, face_matrix=faces, v_normals_matrix=vnorms, vertex_quality_matrix=vals)

TypeError: __init__(): incompatible constructor arguments. The following argument types are supported:
    1. pymeshlab.pmeshlab.Mesh(vertex_matrix: numpy.ndarray[numpy.float32[m, 3]] = array([], shape=(0, 3), dtype=float32), face_matrix: numpy.ndarray[numpy.int32[m, 3]] = array([], shape=(0, 3), dtype=int32), v_normals_matrix: numpy.ndarray[numpy.float32[m, 3]] = array([], shape=(0, 3), dtype=float32), f_normals_matrix: numpy.ndarray[numpy.float32[m, 3]] = array([], shape=(0, 3), dtype=float32))
...

So it seems like vertex_quality_matrix is not something that can be set at instantiation.

So if we can't assign a quality value to vertices and we can't create a mesh with them, how can I associate and arbitrary quality value with each vertex?

My eventual goal is to color the mesh according to these values and then export in the u3d format.

I am using pymeshlab 0.1.9.
Thanks for your time!

[alemuntoni]

Setting per vertex and per face quality in a mesh cannot be done right now. As you can see in the documentation a mesh can be created from scratch passing vertex coords, vertex normals, faces and face normals; quality is missing right now. Generally speaking, all the attributes of the Mesh are read only, and they can be modified only using the method provided by the Mesh class.
I'll add the possibility to set per vertex and per face quality in the mesh construction, in the next pymeshlab version.

[ghost]

Understood, thank you!

[ghost]

Just out of curiosity, how is the quality value normally used? Is it loaded with the file or is it something the user supplies while working in Meshlab? Thanks.

[alemuntoni]

Quality is just a scalar value that is associated to vertices/faces. It should actually represent the quality of a certain vertex/face, but there are lot of ways to define the quality of an element in a mesh. Meshlab (and pymeshlab) provides several filters to compute quality depending on various requirements :)
For further information: https://stackoverflow.com/questions/62348898/describing-the-quality-of-a-mesh-with-meshlab

Btw, I pushed a commit that allows to create a mesh also with quality. It will be available in the next pymeshlab version.
You can check this example that shows how to use this feature!

[ghost]

That's awesome! Thank you!