Python library for loading triangular meshes and doing simple operations on them. Included loaders are binary/ASCII STL and Wavefront (OBJ), included exporters are binary STL or COLLADA. If Assimp/pyassimp are available, meshes can be loaded using the assimp loaders. Note that this requires a version of the assimp python bindings from after September 2014.

• Very fast loading of binary STL files (on 234,230 face mesh, was 24.5x faster than assimp)
• Preview meshes (requires pyglet).
• Calculate face adjacencies quickly (for the same 234,230 face mesh .248 s)
• Calculate cross sections (.146 s)
• Split mesh based on face connectivity, requires networkx (4.96 s) or graph-tool (.584 s)
• Calculate mass properties, including volume, center of mass, and moment of inertia (.246 s)
• Find planar facets (.454 s)
• Find and fix face normals and triangle winding (not fast or robust, 32.05 s)
• Find convex hulls of meshes (.21 s)
• Numerous utility functions, such as transforming points, unitizing vectors, etc.

Requires numpy and networkx, additional functions are available with scipy (>.12), pyglet, and pyassimp

import trimesh

# load_mesh can accept a filename or file object, 
# however file objects require 'file_type' specified (eg. file_type='stl')
mesh = trimesh.load_mesh('./models/unit_cube.STL')

# does basic cleanup of mesh, including merging vertices and removing
# duplicate/degenerate faces
mesh.process()

# split mesh based on connected components
# by default this will only return watertight meshes, but the 
# check can be disabled
meshes = mesh.split() 

# first component  
m      = meshes[0]

# opens opengl preview window of mesh with smooth shading
# smooth shading is disabled automatically for large meshes as it gets slow
m.show()

# find groups of coplanar adjacent faces
facets, facets_area = m.facets(return_area=True)

# display the largest facet of the first mesh
# it may be backwards, so try disabling culling with 'c'
trimesh.Trimesh(vertices = m.vertices, 
                faces    = m.faces[facets[np.argmax(facets_area)]]).show()

In the mesh view window, dragging rotates the view, ctl + drag pans, mouse wheel scrolls, 'z' returns to the base view, 'w' toggles wireframe mode, and 'c' toggles backface culling (useful if viewing non-watertight meshes).