1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
|
"""
.. _extract_surface_example:
Extract Surface
~~~~~~~~~~~~~~~
You can extract the surface of nearly any object within ``pyvista``
using the ``extract_surface`` filter.
"""
# sphinx_gallery_thumbnail_number = 2
from __future__ import annotations
import numpy as np
import pyvista as pv
from pyvista import CellType
# %%
# Create a quadratic cell and extract its surface
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Here we create a single quadratic hexahedral cell and then extract its surface
# to demonstrate how to extract the surface of an UnstructuredGrid.
lin_pts = np.array(
[
[-1, -1, -1], # point 0
[1, -1, -1], # point 1
[1, 1, -1], # point 2
[-1, 1, -1], # point 3
[-1, -1, 1], # point 4
[1, -1, 1], # point 5
[1, 1, 1], # point 6
[-1, 1, 1], # point 7
],
np.double,
)
# these are the "midside" points of a quad cell. See the definition of a
# vtkQuadraticHexahedron at:
# https://vtk.org/doc/nightly/html/classvtkQuadraticHexahedron.html
quad_pts = np.array(
[
(lin_pts[1] + lin_pts[0]) / 2, # between point 0 and 1
(lin_pts[1] + lin_pts[2]) / 2, # between point 1 and 2
(lin_pts[2] + lin_pts[3]) / 2, # and so on...
(lin_pts[3] + lin_pts[0]) / 2,
(lin_pts[4] + lin_pts[5]) / 2,
(lin_pts[5] + lin_pts[6]) / 2,
(lin_pts[6] + lin_pts[7]) / 2,
(lin_pts[7] + lin_pts[4]) / 2,
(lin_pts[0] + lin_pts[4]) / 2,
(lin_pts[1] + lin_pts[5]) / 2,
(lin_pts[2] + lin_pts[6]) / 2,
(lin_pts[3] + lin_pts[7]) / 2,
],
)
# introduce a minor variation to the location of the mid-side points
# seed the random numbers for reproducibility
rng = np.random.default_rng(seed=0)
quad_pts += rng.random(quad_pts.shape) * 0.3
pts = np.vstack((lin_pts, quad_pts))
# create the grid
cells = np.hstack((20, np.arange(20))).astype(np.int64, copy=False)
celltypes = np.array([CellType.QUADRATIC_HEXAHEDRON])
grid = pv.UnstructuredGrid(cells, celltypes, pts)
# finally, extract the surface and plot it
surf = grid.extract_surface()
surf.plot(show_scalar_bar=False)
# %%
# Nonlinear Surface Subdivision
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Should your UnstructuredGrid contain quadratic cells, you can
# generate a smooth surface based on the position of the
# "mid-edge" nodes. This allows the plotting of cells
# containing curvature. For additional reference, please see:
# https://prod.sandia.gov/techlib-noauth/access-control.cgi/2004/041617.pdf
surf_subdivided = grid.extract_surface(nonlinear_subdivision=5)
surf_subdivided.plot(show_scalar_bar=False)
|
