pyckingsolver 0.1.2

Shapely-based Python interface for PackingSolver — 2D irregular bin packing & nesting

pyckingsolver

Shapely-based Python interface for PackingSolver — 2D irregular bin packing & nesting.

Pack irregular shapes into bins — rectangles, circles, arbitrary polygons with holes. Built for CNC laser cutting, sheet metal nesting, fabric cutting, and any 2D packing problem.

Laser cutting layout: mounting plates with bolt holes, washers, U-brackets, discs & gussets

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Install

pip install pyckingsolver

The C++ solver binary is bundled — no compilation needed on Windows x64 and Linux x64.

For other platforms, build the solver from the included submodule. See Building the Solver.

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Gallery

Hole Fill	Custom Holes & Rings	Metal Cutting
Filler placed inside frame hole	Frames, rings, discs & triangles	Plates, washers, brackets & gussets

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Quick Start

from shapely.geometry import Polygon, Point
from pyckingsolver import InstanceBuilder, Objective, Solver

b = InstanceBuilder(Objective.OPEN_DIMENSION_X)
b.add_bin_type_rectangle(1200, 600)
b.add_item_type_rectangle(80, 60, copies=10)
b.add_item_type(Polygon([(0,0),(50,0),(25,40)]), copies=6)

solver = Solver()  # auto-finds bundled binary
solution = solver.solve(b.build(), time_limit=30)

print(f"{solution.total_item_count()} items in {solution.total_bins_used()} bins")

for item in solution.all_items():
    print(item.item_type_id, item.angle, item.shapes[0].bounds)

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Objectives

Choose what the solver optimizes:

Objective	Use Case
OPEN_DIMENSION_X	Minimize strip width — items pack left-to-right (laser cutting rolls)
OPEN_DIMENSION_Y	Minimize strip height
OPEN_DIMENSION_XY	Minimize both dimensions (compact 2D nesting)
BIN_PACKING	Use fewest bins — fixed-size sheets
KNAPSACK	Maximize value of items in one bin
VARIABLE_SIZED_BIN_PACKING	Multiple bin sizes with costs — minimize total cost
BIN_PACKING_WITH_LEFTOVERS	Bin packing that tracks reusable scrap

from pyckingsolver import Objective

b = InstanceBuilder(Objective.BIN_PACKING)

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InstanceBuilder

Bins

b = InstanceBuilder(Objective.BIN_PACKING)

# Rectangle bin
b.add_bin_type_rectangle(1200, 600, copies=10, cost=1.0)

# Circle bin
b.add_bin_type_circle(radius=300, resolution=64)

# Any Shapely polygon
b.add_bin_type(Polygon([...]))

# With edge clearance (e.g. clamp margin)
b.add_bin_type_rectangle(1200, 600, item_bin_minimum_spacing=5.0)

# Multiple bin types (variable-sized bin packing)
small_id = b.add_bin_type_rectangle(600, 400, cost=1.0, copies=5)
large_id = b.add_bin_type_rectangle(1200, 800, cost=1.8, copies=3)

Items

# Rectangle item
b.add_item_type_rectangle(80, 60, copies=4)

# Any Shapely polygon
b.add_item_type(Polygon([(0,0),(100,0),(50,80)]), copies=6)

# Polygon with interior hole (e.g. washer, frame)
washer = Point(0,0).buffer(30).difference(Point(0,0).buffer(15))
b.add_item_type(washer, copies=4)

# With profit (for knapsack)
b.add_item_type(polygon, copies=3, profit=42.0)

# Multiple shapes per item (composite/multi-part item)
b.add_item_type([shape_a, shape_b], copies=2)

Rotations

# Fixed (no rotation) — default
b.add_item_type(shape, allowed_rotations=[(0, 0)])

# 90° increments
b.add_item_type(shape, allowed_rotations=[(0,0),(90,90),(180,180),(270,270)])

# Any custom discrete angles
b.add_item_type(shape, allowed_rotations=[(0,0),(45,45),(90,90)])

# Free continuous rotation
b.add_item_type(shape, allowed_rotations=[(0, 360)])

# Mirroring
b.add_item_type(shape, allow_mirroring=True)

Spacing

# Minimum gap between all items (e.g. 2mm laser kerf)
b.set_item_item_minimum_spacing(2.0)

# Clearance from bin edges (per bin type)
b.add_bin_type_rectangle(1200, 600, item_bin_minimum_spacing=5.0)

Defects

Defects are no-go zones inside a bin (scratches, holes, clamps):

bin_id = b.add_bin_type_rectangle(1200, 600)

# Add a defect (no item may overlap it)
scratch = Polygon([(100,100),(200,100),(200,150),(100,150)])
b.add_defect(bin_id, scratch)

# With clearance around defect
b.add_defect(bin_id, scratch, item_defect_minimum_spacing=3.0)

# With defect type label
b.add_defect(bin_id, scratch, defect_type=1)

Quality Rules

Restrict certain items to certain zones of the bin:

b.add_quality_rule([0, 1])        # items with quality_rule=0 can go on areas 0 or 1
b.add_item_type(shape, copies=2)  # quality_rule=-1 = no restriction (default)

Aspect Ratio (Open Dimension XY)

b = InstanceBuilder(Objective.OPEN_DIMENSION_XY)
b.set_open_dimension_xy_aspect_ratio(1.5)  # enforce width/height <= 1.5

Leftover Corner

For BIN_PACKING_WITH_LEFTOVERS, set the reference corner for scrap:

from pyckingsolver import Corner

b.set_leftover_corner(Corner.BOTTOM_LEFT)   # default
b.set_leftover_corner(Corner.TOP_RIGHT)

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Use Cases

Laser Cutting / Sheet Metal Nesting

Minimize material usage from a fixed sheet with kerf spacing:

from shapely.geometry import Polygon, Point
from pyckingsolver import InstanceBuilder, Objective, Solver

b = InstanceBuilder(Objective.BIN_PACKING)
b.set_item_item_minimum_spacing(2.0)        # 2mm laser kerf
b.add_bin_type_rectangle(1200, 600, copies=100)

# Mounting plate with bolt holes
plate = Polygon([(0,0),(150,0),(150,100),(0,100)])
for cx, cy in [(25,25),(125,25),(25,75),(125,75)]:
    plate = plate.difference(Point(cx,cy).buffer(12, resolution=16))
b.add_item_type(plate, copies=8,
                allowed_rotations=[(0,0),(90,90),(180,180),(270,270)])

# Discs that nest inside the bolt holes
b.add_item_type(Point(0,0).buffer(8, resolution=16), copies=16)

# L-bracket
b.add_item_type(
    Polygon([(0,0),(80,0),(80,60),(70,60),(70,10),(10,10),(10,60),(0,60)]),
    copies=12, allowed_rotations=[(0,0),(90,90),(180,180),(270,270)])

solution = Solver().solve(b.build(), time_limit=60)
print(f"{solution.total_item_count()} parts in {solution.total_bins_used()} sheets")

Roll / Strip Cutting

Minimize roll length consumed:

b = InstanceBuilder(Objective.OPEN_DIMENSION_X)
b.set_item_item_minimum_spacing(1.5)
b.add_bin_type_rectangle(99999, 1200)   # very long, fixed width

b.add_item_type(shape_a, copies=20, allowed_rotations=[(0, 360)])
b.add_item_type(shape_b, copies=15, allowed_rotations=[(0, 360)])

solution = Solver().solve(b.build(), time_limit=30)
used_length = max(item.x + item.shapes[0].bounds[2]
                  for item in solution.all_items())
print(f"Roll used: {used_length:.1f} mm")

Knapsack / Value Maximization

Pack as much value as possible in one bin:

b = InstanceBuilder(Objective.KNAPSACK)
b.add_bin_type_rectangle(500, 300)

shapes_with_values = [
    (Polygon([...]), 10.0),
    (Polygon([...]), 25.0),
]
for shape, profit in shapes_with_values:
    b.add_item_type(shape, copies=5, profit=profit)

solution = Solver().solve(b.build(), time_limit=30)
total_profit = sum(
    instance.item_types[item.item_type_id].profit
    for item in solution.all_items()
)

Variable-Sized Bin Packing

Choose from multiple sheet sizes to minimize cost:

b = InstanceBuilder(Objective.VARIABLE_SIZED_BIN_PACKING)
b.add_bin_type_rectangle(600, 400, cost=1.0, copies=10)
b.add_bin_type_rectangle(1200, 800, cost=1.8, copies=5)

for shape in my_parts:
    b.add_item_type(shape, copies=2)

solution = Solver().solve(b.build(), time_limit=60)

Defective Sheet Handling

Avoid defective zones on material:

b = InstanceBuilder(Objective.BIN_PACKING)
bin_id = b.add_bin_type_rectangle(1200, 600)

# Scratch at center — no item within 3mm
scratch = Point(600,300).buffer(40)
b.add_defect(bin_id, scratch, item_defect_minimum_spacing=3.0)

# Clamped edges — keep items 10mm from edges
b.add_bin_type_rectangle(1200, 600, item_bin_minimum_spacing=10.0)

Arbitrary Polygon Bins

Non-rectangular cutting areas (e.g., round table, irregular offcut):

# Circular bin
b.add_bin_type_circle(radius=500)

# Hexagonal bin
import math
hex_pts = [(500*math.cos(math.pi/3*i), 500*math.sin(math.pi/3*i)) for i in range(6)]
b.add_bin_type(Polygon(hex_pts))

# Irregular offcut
offcut = Polygon([(0,0),(800,0),(800,300),(500,600),(0,600)])
b.add_bin_type(offcut)

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Solver

from pyckingsolver import Solver

# Auto-discover bundled binary
solver = Solver()

# Explicit binary path
solver = Solver(binary="path/to/packingsolver_irregular")

# Different problem type (rectangle-only problems)
solver = Solver(problem_type="rectangle")

solution = solver.solve(
    instance,
    time_limit=60,              # seconds
    verbosity_level=1,          # 0=quiet, 1=summary, 2=verbose
    output_path="sol.json",     # optional: persist solution JSON
    extra_args=["--flag"],      # pass extra CLI args to solver
)

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Solution

solution.total_item_count()     # int: total items placed
solution.total_bins_used()      # int: total bins used
solution.all_items()            # list[SolutionItem]: flat, across all bins

for sbin in solution.bins:
    sbin.bin_type_id            # which bin type
    sbin.copies                 # copies of this bin used
    sbin.items                  # list[SolutionItem]

for item in solution.all_items():
    item.item_type_id           # which item type
    item.x, item.y              # placement position
    item.angle                  # rotation in degrees
    item.mirror                 # bool: mirrored?
    item.shapes                 # list[Polygon] — absolute coordinates, ready to use

Export to DXF / SVG / other formats

import ezdxf  # pip install ezdxf

doc = ezdxf.new()
msp = doc.modelspace()
for item in solution.all_items():
    for poly in item.shapes:
        pts = list(poly.exterior.coords)
        msp.add_lwpolyline(pts, close=True)
doc.saveas("output.dxf")

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JSON I/O

Compatible with the C++ solver's JSON format:

# Save/load instance
instance.to_json("problem.json")
instance = Instance.from_json("problem.json")

# Dict round-trip (for custom serialization)
d = instance.to_dict()
instance = Instance.from_dict(d)

# Load / save solution
solution = Solution.from_json("solution.json")

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Geometry Helpers

from pyckingsolver import (
    shapely_to_polygon_json,        # Shapely Polygon → solver JSON dict
    json_shape_to_shapely,          # solver JSON dict → Shapely Polygon
    json_shape_with_holes_to_shapely,  # with interior holes
    elements_to_shapely,            # line-segment + arc elements → Shapely
    circle_to_polygon,              # circle → polygon approximation
)

# Convert arc-based C++ geometry to Shapely
poly = elements_to_shapely(elements, arc_resolution=64)

# Approximate circle
circle = circle_to_polygon(radius=50, center=(100, 100), resolution=64)

# Export any Shapely polygon back to solver JSON
data = shapely_to_polygon_json(my_polygon)  # CCW winding enforced automatically

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Building the Solver

Pre-built binaries are bundled in the pip wheel for Windows x64 and Linux x64.

For other platforms, build from the included submodule:

git clone --recurse-submodules https://github.com/HamzaYslmn/pyckingsolver.git
cd pyckingsolver/extern/packingsolver

# Ubuntu: sudo apt-get install liblapack-dev libbz2-dev
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --config Release --parallel

# Binary location:
# Linux:   extern/packingsolver/build/src/irregular/packingsolver_irregular
# Windows: extern/packingsolver/build/src/irregular/Release/packingsolver_irregular.exe

Then point the solver at it:

solver = Solver(binary="extern/packingsolver/build/src/irregular/packingsolver_irregular")

Updating the C++ Solver

git -C extern/packingsolver pull origin master
git add extern/packingsolver
git commit -m "Update solver submodule"

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How It Works

Python (Shapely)  →  JSON  →  C++ Solver  →  JSON  →  Python (Shapely)
  InstanceBuilder   instance   optimize     solution    Solution

1. Build — define bins and items as Shapely Polygons via InstanceBuilder
2. Serialize — convert to PackingSolver JSON (CCW winding enforced, holes as interior rings)
3. Solve — C++ solver runs branch-and-bound / heuristics
4. Parse — placed items returned as Shapely geometries in absolute coordinates

The C++ solver (fontanf/packingsolver) also supports rectangle, box (3D), guillotine cut, and 1D packing — accessible by passing problem_type to Solver().

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License

MIT — see LICENSE.

Based on PackingSolver by Florian Fontan.