Volumetric meshes, such as tetrahedral (tet) and hexahedral (hex, cube-like) meshes, represent a region of 3D space. Polyscope can display tet and hex meshes, including those which have a mix of hex and tet elements. We'll use the term cell to refer generically to a tet or hex in a volume mesh. As always, Polyscope can also handle scalar, color, or vector quantities associated with the vertices or cells of the mesh, and you can click on the mesh elements to inspect values.
Example: registering a tetrahedral mesh
import polyscope as ps
import numpy as np
import igl
verts, tets, _ = igl.read_mesh("my_mesh.mesh")
ps_vol = ps.register_volume_mesh("test volume mesh", verts, tets=tets)
n_vert = verts.shape[0]
n_cell = tets.shape[0]
# Add a scalar function on vertices
data_vert = np.random.rand(n_vert)
ps_vol.add_scalar_quantity("my vertex val", data_vert)
# you can also access the structure by name
ps.get_volume_mesh("test volume mesh").add_scalar_quantity("my vertex val", data_vert)
# Add a scalar function on cells (with some options set)
data_cell = np.random.rand(n_cell)
ps_vol.add_scalar_quantity("my cell val", data_cell, defined_on='cells',
vminmax=(-3., 3.), cmap='blues')
# Show the GUI
ps.show() Volume meshes are registered with Polyscope by passing the location of each vertex in the mesh, as well as the vertex indices for each cell. There are a few different argument variants to register meshes with tets, hexes, or a mix of the two.
???+ func "#!python register_volume_mesh(name, vertices, tets=None, hexes=None, mixed_cells=None, enabled=None, color=None, interior_color=None, edge_color=None, edge_width=None, material=None)"
Add a new volume mesh structure to Polyscope.
- `name` string, a name for the structure
- `vertices` an `Nx3` numpy float array of vertex locations
The elements are specified by a combination of the following arguments:
- `tets` a `Tx4` numpy integer array of tetrahedra, as 0-based indices in to the vertices array
- `hexes` a `Hx8` numpy integer array of hexahedra, as 0-based indices in to the vertices array
- `mixed_cells` a `Mx8` numpy integer array which may contain a mix of tetrahedra and hexahedra. For any rows which are tets and thus have just 4 indices, the remaining indices should be set to any negative value.
You may pass in `tets`, `hexes`, or both to specify the connectivty. Alternately, `mixed_cells` may be used. However, it is not supported to specify both `tets`/`hexes` and `mixed_cells`. For the purposes of element ordering, when `tets` and `hexes` are both passed, the cells are presumed to be ordered with all tetrahedral cells coming first, then hexahedral cells.
Additional optional keyword arguments:
- `enabled` boolean, is the structure enabled initially
- `color` float 3-tuple, default color values for the outside of the mesh as rgb in [0,1]
- `interior_color` float 3-tuple, default color values for the inside of the mesh as rgb in [0,1]
- `edge_color` float 3-tuple, default color values for edges of the mesh as rgb in [0,1] (be sure to set `edge_width` too)
- `edge_width` float, width of edges in rendered mesh; default sets `0` to disable edges, `1` is a reasonable value to enable
- `material` string, name of material to use for the mesh
if not specified, these optional parameters will assume a reasonable default value, or a [persistant value](../../../basics/parameters/#persistent-values) if previously set.
!!! warning "No support for 2D"
Unlike other structures, 2D volume meshes are not supported; they don't make much sense (see [2D data]([[url.prefix]]/features/2D_data)).
The locations of the vertices in a mesh can be updated with the member function update_vertex_positions(newPositions). All quantities will be preserved. Changing the connectivity or element counts in a mesh is not supported, you will need to register a new mesh (perhaps with the same name to overwrite).
??? func "#!python VolumeMesh.update_vertex_positions(newPos)"
Update the vertex positions in a volume mesh structure. `newPos` must be valid input to initially construct the vertex positions, with the same number of vertices.
Slice planes are particularly useful for inspecting the internal stucture of a volume mesh, as shown in the demo video at the top. Slice planes can be manipulated programmatically or manually in the GUI; they also have special functionality for filling in sliced data for volume meshes. See the slice plane documentation for more details.
Options control the appearance of the mesh. Note that these options can also be passed as keyword arguments to the initial register_volume_mesh(), as noted above.
| Parameter | Meaning | Getter | Setter | Persistent? |
|---|---|---|---|---|
| enabled | is the structure enabled? | #!python bool is_enabled() |
#!python set_enabled(newVal) |
yes |
| transparency | alpha value | #!python get_transparency() |
#!python set_transparency(newVal) |
yes |
| color | the color of the outside of the volume | #!python get_color() |
#!python set_color(val) |
yes |
| interior color | the color of the inside of the volume | #!python get_interior_color() |
#!python set_interior_color(val) |
yes |
| edge color | the color of the edges of the mesh | #!python get_edge_color() |
#!python set_edge_color(val) |
yes |
| edge width | how thick to draw mesh edges, use 0. to disable and 1. for reasonable edges |
#!python get_edge_width() |
#!python set_edge_width(val) |
yes |
| material | what material to use | #!python get_material() |
#!python set_material(name) |
yes |
Example: set options which affect the appearance of the mesh
import numpy as np
import polyscope as ps
# a simple inline mesh
verts = np.array([
[0, 0, 0],
[1, 0, 0],
[1, 1, 0],
[0, 1, 0],
[0, 0, 1],
[1, 0, 1],
[1, 1, 1],
[0, 1, 1],
[1, 1, 1.5]
])
cells = np.array([
[0, 1, 2, 3, 4, 5, 6, 7],
[7, 5, 6, 8, -1, -1, -1, -1],
])
ps_vol = ps.register_volume_mesh("test volume mesh", verts, mixed_cells=cells)
ps_vol.set_enabled(False) # disable
ps_vol.set_enabled() # default is true
ps_vol.set_color((0.3, 0.6, 0.8)) # rgb triple on [0,1]
ps_vol.set_interior_color((0.4, 0.7, 0.9))
ps_vol.set_edge_color((0.8, 0.8, 0.8))
ps_vol.set_edge_width(1.0)
ps_vol.set_material("wax")
ps_vol.set_transparency(0.5)
# alternately:
ps.register_volume_mesh("test volume mesh 2", verts, mixed_cells=cells, enabled=False,
color=(1., 0., 0.), interior_color=(0., 1., 0.),
edge_color=((0.8, 0.8, 0.8)), edge_width=1.0,
material='candy', transparency=0.5)
ps.show()