Create Triangulated Surface

Create a surface from a set of points through a Delaunay triangulation. This example uses pyvista.PolyDataFilters.delaunay_2d().

from __future__ import annotations

import numpy as np

import pyvista as pv

# Seed random numbers for reproducibility
rng = np.random.default_rng(seed=0)

Simple Triangulations

First, create some points for the surface.

# Define a simple Gaussian surface
n = 20
x = np.linspace(-200, 200, num=n) + rng.uniform(-5, 5, size=n)
y = np.linspace(-200, 200, num=n) + rng.uniform(-5, 5, size=n)
xx, yy = np.meshgrid(x, y)
A, b = 100, 100
zz = A * np.exp(-0.5 * ((xx / b) ** 2.0 + (yy / b) ** 2.0))

# Get the points as a 2D NumPy array (N by 3)
points = np.c_[xx.reshape(-1), yy.reshape(-1), zz.reshape(-1)]
points[0:5, :]

array([[-198.63038313, -204.71680329,    1.71090121],
       [-181.24950128, -204.71680329,    2.38012408],
       [-162.4850016 , -204.71680329,    3.28594053],
       [-141.67682891, -204.71680329,    4.5091358 ],
       [-112.65677129, -204.71680329,    6.52176016]])

Now use those points to create a point cloud PyVista data object. This will be encompassed in a pyvista.PolyData object.

# simply pass the numpy points to the PolyData constructor
cloud = pv.PolyData(points)
cloud.plot(point_size=15)

Static Scene

Interactive Scene

Now that we have a PyVista data structure of the points, we can perform a triangulation to turn those boring discrete points into a connected surface.

surf = cloud.delaunay_2d()
surf.plot(show_edges=True)

Static Scene

Interactive Scene

Masked Triangulations

x = np.arange(10, dtype=float)
xx, yy, zz = np.meshgrid(x, x, [0])
points = np.column_stack((xx.ravel(order='F'), yy.ravel(order='F'), zz.ravel(order='F')))
# Perturb the points
points[:, 0] += rng.random(len(points)) * 0.3
points[:, 1] += rng.random(len(points)) * 0.3
# Create the point cloud mesh to triangulate from the coordinates
cloud = pv.PolyData(points)
cloud

PolyData	Information
N Cells	100
N Points	100
N Strips	0
X Bounds	2.520e-02, 9.288e+00
Y Bounds	2.986e-03, 9.297e+00
Z Bounds	0.000e+00, 0.000e+00
N Arrays	0

Run the triangulation on these points

surf = cloud.delaunay_2d()
surf.plot(cpos='xy', show_edges=True)

Static Scene

Interactive Scene

Note that some of the outer edges are unconstrained and the triangulation added unwanted triangles. We can mitigate that with the alpha parameter.

surf = cloud.delaunay_2d(alpha=1.0)
surf.plot(cpos='xy', show_edges=True)

Static Scene

Interactive Scene

We could also add a polygon to ignore during the triangulation via the edge_source parameter.

# Define a polygonal hole with a clockwise polygon
ids = [22, 23, 24, 25, 35, 45, 44, 43, 42, 32]

# Create a polydata to store the boundary
polygon = pv.PolyData()
# Make sure it has the same points as the mesh being triangulated
polygon.points = points
# But only has faces in regions to ignore
polygon.faces = np.insert(ids, 0, len(ids))

surf = cloud.delaunay_2d(alpha=1.0, edge_source=polygon)

p = pv.Plotter()
p.add_mesh(surf, show_edges=True)
p.add_mesh(polygon, color='red', opacity=0.5)
p.show(cpos='xy')

Static Scene

Interactive Scene

Tags: load