compas_cgal.isolines

Isoline extraction from vertex scalar fields using CGAL.

Functions

isolines

isolines(
    mesh: Mesh,
    scalars: str,
    isovalues: list[float] | None = None,
    n: int | None = None,
    resample: int | bool = True,
    smoothing: int = 0,
) -> PolylinesNumpy

Extract isoline polylines from vertex scalar field.

Uses CGAL's refine_mesh_at_isolevel to extract isolines from a scalar field defined at mesh vertices.

Parameters:

Name	Type	Description	Default
mesh	:class:`compas.datastructures.Mesh`	A triangulated mesh.	required
scalars	str	Name of the vertex attribute containing scalar values.	required
isovalues	list[float]	Explicit isovalue thresholds for isoline extraction.	None
n	int	Number of evenly spaced isovalues between scalar min and max. The isovalues will exclude the endpoints.	None
resample	int or bool	Polyline resampling mode. If True (default), adaptively resample segments longer than 2x median length. If int > 1, uniformly subdivide each segment into that many parts. If False or 1, disable.	True
smoothing	int	Number of Laplacian smoothing iterations to apply to polylines. Default is 0 (no smoothing).	0

Returns:

Type	Description
attr:`compas_cgal.types.PolylinesNumpy`	List of polyline segments as Nx3 arrays of points.

Raises:

Type	Description
ValueError	If neither or both of isovalues and n are provided.

Examples:

>>> from compas.datastructures import Mesh
>>> from compas.geometry import Sphere
>>> from compas_cgal.geodesics import heat_geodesic_distances
>>> from compas_cgal.isolines import isolines
>>> sphere = Sphere(1.0)
>>> mesh = Mesh.from_shape(sphere, u=32, v=32)
>>> mesh.quads_to_triangles()
>>> vf = mesh.to_vertices_and_faces()
>>> distances = heat_geodesic_distances(vf, [0])
>>> for key, d in zip(mesh.vertices(), distances):
...     mesh.vertex_attribute(key, "distance", d)
>>> polylines = isolines(mesh, "distance", n=5)