3D mesh plot

  New in version 24.09.2.

This notebook illustrates how to render 3D meshes by supplying a list of vertex positions and vertex indices to construct the mesh faces.

import scipp as sc
import plopp as pp
from plopp.data import examples

Loading mesh data

We load a file containing the data to construct the Utah teapot (see below for a description of the data format).

dg = sc.io.load_hdf5(examples.teapot())
dg

Downloading file 'teapot.h5' from 'https://public.esss.dk/groups/scipp/plopp/1/teapot.h5' to '/home/runner/.cache/plopp/1'.

scipp.DataGroup

(pix: None)

• vertices

  scipp

  Variable

  (pix: 137)

  vector3

  m

  [ 7. 0. 12.], [ 4.97 -4.97 12. ], ..., [ 2.9288 2.9288 12.75 ], [ 4.615 4.615 12. ]
• faces

  scipp

  Variable

  (pix: 720)

  int64

  𝟙

  0, 1, ..., 135, 124

Creating a mesh plot

We can now send the data to the `mesh3d <../../generated/plopp.mesh3d.html>`__ function for rendering (we color the mesh according to z position):

pp.mesh3d(
    vertices=dg["vertices"],
    faces=dg["faces"],
    vertexcolors=dg["vertices"].fields.z,
)

Adding mesh edges

It is also possible to show the edges of the mesh using the edgecolor argument:

pp.mesh3d(
    vertices=dg["vertices"],
    faces=dg["faces"],
    vertexcolors=dg["vertices"].fields.z,
    edgecolor="black",
)

The data format

The data used above contains a list of vertices (position vectors in 3d space), and a list of faces which define how the vertices are connected to each other.

The faces is a flat list of sequences of 3 indices that code for vertices which make up mesh triangles.

As an example, we will construct a simple tetrahedric mesh.

vertices = sc.vectors(
    dims=["vertices"],
    values=[[-1, 0, 0], [0.7, 0, 1], [0.7, 0, -1], [0, 1.3, 0]],
    unit="m",
)
faces = sc.array(
    dims=["faces"],
    values=[
        # First triangle
        0, 1, 3,
        # Second triangle
        1, 2, 3,
        # Third triangle
        2, 0, 3,
        # Fourth triangle
        0, 2, 1,
    ],
)

pp.mesh3d(
    vertices=vertices,
    faces=faces,
    edgecolor="black",
)

You can then also add colors on the vertices:

pp.mesh3d(
    vertices=vertices,
    faces=faces,
    vertexcolors=vertices.fields.x,
    edgecolor="black",
)