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Measuring and analysis

Measures​

from smlibpy import *

part = Box(40, 30, 20) - Cylinder(6, 30)

part.volume              # 24000 - pi * 36 * 20
part.area                # total surface area
part.center()            # center of mass
part.bbox()              # BoundBox: .min, .max, .size, .center
part.is_valid()          # a closed, manifold solid with a positive volume?
part.info()              # counts and bounding box in one dict

face = part.faces().top().one()
face.area, face.center(), face.normal_at(), face.geom_type

edge = part.edges().circles().first
edge.length, edge.radius, edge.arc_center, edge.point_at(0.25), edge.tangent_at(0.25)

Areas, volumes and centers come from numerical integration over the exact NURBS geometry, to a relative accuracy of 1e-7 by default (smlibpy.shapes.ACCURACY). They do not depend on a mesh.

Mass properties​

mp = part.mass_properties(density=7.85e-3)     # steel in g/mm³ gives grams
mp.mass
mp.center                  # center of mass
mp.inertia                 # 3x3 inertia tensor about the center of mass
mp.principal_moments
mp.principal_axes

precise = part.mass_properties(density=7.85e-3, accuracy=1e-10)

Distances​

a = Box(10, 10, 10)
b = Sphere(3).translate(20, 0, 0)
a.distance_to(b)                 # 12.0
a.distance_to((0, 0, 30))        # to a point
a.closest_point((0, 0, 30))      # Vector(0, 0, 5)

Intersections and projections​

box = Box(20, 20, 20)
pipe = Cylinder(4, 40).rotate(X, 30)

box.intersection_curves(pipe)               # where the surfaces cross, as edges
Sphere(10).silhouette((0, 0, 1))            # outline seen along a direction
box.project(CenterArc((0, 0, 30), 5, 0, 360), (0, 0, -1))   # curve onto the faces below
box.outline(Plane.XZ)                       # edges projected to a plane
Line((0, 0), (10, 10)).intersections(Line((0, 10), (10, 0)))  # [Vector(5, 5, 0)]

Meshes​

tessellate (or shape.mesh()) turns exact shapes into triangles, with a tolerance on the distance to the true surface:

mesh = part.mesh(tolerance=0.01)
mesh.vertices, mesh.triangles          # numpy arrays
mesh.volume, mesh.area, len(mesh)

Meshes made by tessellate also take +, - and &, but the kernel's mesh Booleans only work where no face of the result gets a hole. The result is checked (closed, a volume the operation can give) and a wrong one raises ModelingError. Do Booleans on the exact parts and mesh the result:

blob = (Box(10, 10, 10) - Sphere(6)).mesh()
print(blob.is_closed(), round(blob.volume, 1))