NumPy-STL Processing

Process STL files with numpy-based mesh operations.

Installation

pip install numpy-stl

Reading and Writing STL

from stl import mesh
import numpy as np

# Load STL file
your_mesh = mesh.Mesh.from_file('model.stl')

# Save STL file
your_mesh.save('output.stl')

# Save as ASCII STL
your_mesh.save('output.stl', mode=mesh.Mode.ASCII)

Creating Meshes from Scratch

from stl import mesh
import numpy as np

# Define vertices of a cube
vertices = 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]
])

# Define 12 triangles (2 per face)
faces = np.array([
    [0,3,1], [1,3,2],  # bottom
    [4,5,7], [5,6,7],  # top
    [0,1,5], [0,5,4],  # front
    [2,3,7], [2,7,6],  # back
    [0,4,7], [0,7,3],  # left
    [1,2,6], [1,6,5],  # right
])

# Create mesh
cube = mesh.Mesh(np.zeros(faces.shape[0], dtype=mesh.Mesh.dtype))
for i, f in enumerate(faces):
    for j in range(3):
        cube.vectors[i][j] = vertices[f[j]]

cube.save('cube.stl')

Mesh Transformations

from stl import mesh
import numpy as np

m = mesh.Mesh.from_file('model.stl')

# Translation
m.translate([10, 0, 0])

# Rotation (around Z axis, 45 degrees)
m.rotate([0, 0, 1], np.radians(45))

# Uniform scaling
m.vectors *= 2.0

# Non-uniform scaling
m.x *= 2.0
m.y *= 1.5

Mesh Analysis

from stl import mesh

m = mesh.Mesh.from_file('model.stl')

# Volume and center of mass
volume, cog, inertia = m.get_mass_properties()
print(f"Volume: {volume}")
print(f"Center of mass: {cog}")

# Bounding box
minx, maxx = m.x.min(), m.x.max()
miny, maxy = m.y.min(), m.y.max()
minz, maxz = m.z.min(), m.z.max()

# Surface area
areas = m.areas
total_area = np.sum(areas)

# Number of triangles
num_triangles = len(m.vectors)

Combining Meshes

from stl import mesh
import numpy as np

mesh1 = mesh.Mesh.from_file('part1.stl')
mesh2 = mesh.Mesh.from_file('part2.stl')

# Translate second mesh
mesh2.translate([20, 0, 0])

# Combine
combined = mesh.Mesh(np.concatenate([mesh1.data, mesh2.data]))
combined.save('combined.stl')

Mesh Repair Checks

from stl import mesh

m = mesh.Mesh.from_file('model.stl')

# Check normals
m.update_normals()

# Check if mesh is closed (watertight)
# Count edges that appear only once
from collections import Counter

def get_edges(m):
    edges = []
    for triangle in m.vectors:
        for i in range(3):
            edge = tuple(sorted([tuple(triangle[i]), tuple(triangle[(i+1)%3])]))
            edges.append(edge)
    return edges

edge_counts = Counter(get_edges(m))
open_edges = [e for e, c in edge_counts.items() if c == 1]
is_watertight = len(open_edges) == 0