How to access point data for a cell? about pyvista-support

[banesullivan]

FYI, a true PyVista version of this would be:

import pyvista as pv
from pyvista import examples
import numpy as np

poly_data = examples.download_doorman()

clipped = poly_data.clip(normal=[1,0,0], 
                         origin=poly_data.center, 
                         invert=False)

clipped.plot()

Then, you could grab the cell nodes like so (if I understand this correctly... if not, @S0Phon, would you please post your solution):

cell_indices = clipped.faces
# make sure all triangles
assert not cell_indices.size % 4 and np.all(cell_indices.reshape(-1, 4)[:,0] == 3)
# Grab ids for all cell nodes
cell_node_ids = cell_indices.reshape(-1, 4)[:,1:4].ravel()

cell_nodes = clipped.points[cell_node_ids]
cell_nodes

array([[1.666226, 3.261832, 0.646217],
       [1.658398, 3.293886, 0.599486],
       [1.615146, 3.251326, 0.649149],
       ...,
       [0.11784 , 5.763801, 0.25697 ],
       [0.126947, 5.757092, 0.256631],
       [0.121833, 5.77197 , 0.242532]], dtype=float32)

[GuillaumeFavelier]

I assume the variable clipped is a vtkPolyData so you can wrap it with:
clipped = pv.PolyData(clipped)
By default, I think it's only a shallow copy but more details can be found in the pyvista.core.PolyData class.

And then you have access to clipped.faces which is a one-dimensional array of cells following VTK convention [cell0_nverts, cell0_v0, cell0_v1, cell0_v2, cell1_nverts, ...]. You can obtain the number of faces by using the clipped.n_faces attribute.

Is it helpful @S0Phon?

btw, I see in the doc it's written that faces returns a pointer to the points as a numpy object, we will correct this (points for points and faces for cells).

[S0Phon]

Thank you for responding. If I understand correctly then I think this is very helpful and has answered my question.
Just to check, are the cell0_v0, cell0_v1 and cell0_v2 etc, indices to the points in the points array given by clipped.points?

[GuillaumeFavelier]

Just to check, are the cell0_v0, cell0_v1 and cell0_v2 etc, indices to the points in the points array given by clipped.points?

Exactly!

[S0Phon]

Great! Thank you again @GuillaumeFavelier . I shall close this issue

[S0Phon]

This is great. Thank you @banesullivan, it is much more concise than what I had done.