cube_example.py

from pymoab import core, types
import numpy as np

# Initialize the PyMOAB core
mb = core.Core()

# Step 1: Create vertices for a unit cube (x, y, z)
vertices_coords = np.array(
    [
        (0, 0, 0),  # Vertex 0
        (1, 0, 0),  # Vertex 1
        (1, 1, 0),  # Vertex 2
        (0, 1, 0),  # Vertex 3
        (0, 0, 1),  # Vertex 4
        (1, 0, 1),  # Vertex 5
        (1, 1, 1),  # Vertex 6
        (0, 1, 1),  # Vertex 7
    ],
    dtype="float64",
).flatten()

vertices = mb.create_vertices(vertices_coords)

# Step 2: Define triangular faces for the cube's 6 surfaces
# Each surface has two triangles
tri_faces = [
    # Bottom face (z = 0)
    (vertices[0], vertices[1], vertices[2]),
    (vertices[0], vertices[2], vertices[3]),
    # Top face (z = 1)
    (vertices[4], vertices[5], vertices[6]),
    (vertices[4], vertices[6], vertices[7]),
    # Front face (y = 0)
    (vertices[0], vertices[1], vertices[5]),
    (vertices[0], vertices[5], vertices[4]),
    # Back face (y = 1)
    (vertices[3], vertices[2], vertices[6]),
    (vertices[3], vertices[6], vertices[7]),
    # Left face (x = 0)
    (vertices[0], vertices[3], vertices[7]),
    (vertices[0], vertices[7], vertices[4]),
    # Right face (x = 1)
    (vertices[1], vertices[2], vertices[6]),
    (vertices[1], vertices[6], vertices[5]),
]

triangles = [mb.create_element(types.MBTRI, face) for face in tri_faces]

# Step 3: Group triangles into surface sets
surface_sets = []
for i in range(6):
    surface_set = mb.create_meshset()
    mb.add_entities(
        surface_set, triangles[i * 2 : i * 2 + 2]
    )  # Add 2 triangles per surface
    surface_sets.append(surface_set)

    # Tag surface sets with GEOM_DIMENSION = 2
    geom_dim_tag = mb.tag_get_handle(
        "GEOM_DIMENSION",
        1,
        types.MB_TYPE_INTEGER,
        types.MB_TAG_DENSE,
        create_if_missing=True,
    )
    mb.tag_set_data(geom_dim_tag, surface_set, 2)

# Step 4: Create a volume and associate the surface sets
volume_set = mb.create_meshset()

# Tag the volume with GEOM_DIMENSION = 3
mb.tag_set_data(geom_dim_tag, volume_set, 3)

# Link the surfaces as children of the volume
for surface_set in surface_sets:
    mb.add_parent_child(volume_set, surface_set)

# Step 5: Save to file
mb.write_file("cube_volume.h5m")

print("Cube volume created and saved to 'cube_volume.h5m'.")