FastBBox

Fast IoU/overlap computations for axis-aligned and oriented bounding boxes, powered by nanobind C++ extensions.

Benchmark

Function Python (ms)    FastBBox (ms)  Speedup
--------------------------------------------------
IoU           1994.19          4.19     475.7x
GIoU          3028.40          5.99     505.8x
DIoU          4104.21          6.21     661.3x
CIoU          6436.51         17.55     366.7x
EIoU          5211.51          7.04     740.5x
NWD           2427.36         13.31     182.4x
OBB          21729.42         31.29     694.5x
--------------------------------------------------
TOTAL        44931.61         85.58     525.1x

Installation

pip install fastbbox

Building from Source

Requires CMake 3.15+ and a C++17 compiler.

git clone https://github.com/gerrylwk/fastbbox
cd fastbbox
pip install .

Usage

Axis-Aligned Bounding Boxes

import numpy as np
from fastbbox import (bbox_overlaps, generalized_iou, distance_iou,
                      complete_iou, efficient_iou, normalized_wasserstein_distance)

# Bounding boxes in [x1, y1, x2, y2] format
boxes = np.array([
    [0, 0, 10, 10],
    [5, 5, 15, 15],
    [20, 20, 30, 30]
], dtype=np.float32)

query_boxes = np.array([
    [0, 0, 10, 10],
    [12, 12, 22, 22]
], dtype=np.float32)

iou = bbox_overlaps(boxes, query_boxes)
giou = generalized_iou(boxes, query_boxes)
diou = distance_iou(boxes, query_boxes)
ciou = complete_iou(boxes, query_boxes)
eiou = efficient_iou(boxes, query_boxes)
nwd = normalized_wasserstein_distance(boxes, query_boxes)

Oriented Bounding Boxes (OBB)

import numpy as np
import math
from fastbbox import bbox_overlaps_obb

# Oriented bounding boxes in [center_x, center_y, width, height, angle_radians] format
obb_boxes = np.array([
    [0, 0, 4, 2, 0],
    [1, 0, 4, 2, math.pi/4],
    [0, 0, 2, 2, math.pi/6],
], dtype=np.float32)

obb_query_boxes = np.array([
    [0, 0, 4, 2, 0],
    [2, 2, 2, 2, 0],
], dtype=np.float32)

obb_iou = bbox_overlaps_obb(obb_boxes, obb_query_boxes)

Features

Axis-Aligned Bounding Box IoU Variants

All variants accept boxes in [x1, y1, x2, y2] top-left-bottom-right format:

• Standard IoU: Classic Intersection over Union
• Generalized IoU (GIoU): Considers enclosing area; values in [-1, 1]
  • Reference: Generalized Intersection over Union
• Distance IoU (DIoU): Penalizes center point distance
  • Reference: Distance-IoU Loss
• Complete IoU (CIoU): Adds aspect ratio consistency penalty to DIoU
  • Reference: Distance-IoU Loss
• Efficient IoU (EIoU): Separate width/height penalties for faster convergence
  • Reference: Focal and Efficient IOU Loss
• Normalized Wasserstein Distance (NWD): Optimal transport-based similarity, values in [0, 1]
  • Effective for tiny object detection
  • Reference: Normalized Gaussian Wasserstein Distance

Oriented Bounding Box (OBB) IoU

Accepts boxes in [center_x, center_y, width, height, angle_radians] format:

• Exact calculation for axis-aligned boxes (angle = 0)
• Approximation-based calculation for rotated boxes using AABB intersection with angle-based scaling
• Batch processing support

Performance

FastBBox provides significant speedup over pure Python implementations, especially for large numbers of bounding boxes.

Run python benchmark_fastbbox.py to benchmark on your system.

When to Use Each Variant

• IoU: Standard evaluation, NMS (Non-Maximum Suppression)
• GIoU: Training loss for non-overlapping boxes
• DIoU: Object detection training where center distance matters
• CIoU: Bounding box regression with aspect ratio consistency
• EIoU: Fast convergence with separate width/height penalties
• NWD: Tiny object detection
• OBB IoU: Rotated object detection, text detection, aerial imagery

OBB Implementation Details

The OBB IoU implementation uses different strategies based on box orientations:

1. Axis-Aligned Boxes (angle = 0): Exact intersection calculation
2. Rotated Boxes: AABB intersection with scaling factor cos(|angle1|) * cos(|angle2|), minimum 50% retention

For exact rotated box IoU, consider implementing Sutherland-Hodgman clipping or the Separating Axes Theorem (SAT).

Development

Building Locally

pip install build scikit-build-core cmake nanobind
python -m build

Testing Your Build

# Correctness tests (compares fastbbox against Python reference implementations)
python test_fastbbox.py              # Summary output
python test_fastbbox.py --verbose    # Detailed output with values
python test_fastbbox.py -f iou giou  # Test specific functions

# Performance benchmarks
python benchmark_fastbbox.py              # Summary output
python benchmark_fastbbox.py --verbose    # Detailed timing per run
python benchmark_fastbbox.py --size 1000  # Test with 1000 boxes
python benchmark_fastbbox.py --runs 10    # 10 iterations

Test File Options

test_fastbbox.py - Correctness validation:

• --verbose, -v: Show detailed output with expected/actual values
• --function, -f: Test specific functions (iou, giou, diou, ciou, eiou, nwd, obb)
• --tolerance, -t: Tolerance threshold (default: 1e-5)
• --obb-tolerance: OBB-specific tolerance (default: 1e-3)
• --size, -s: Number of test boxes (default: 100)

benchmark_fastbbox.py - Performance benchmarks:

• --verbose, -v: Show individual run times and statistics
• --function, -f: Benchmark specific functions
• --size, -s: Number of boxes (default: 500)
• --runs, -r: Number of iterations (default: 5)

Requirements

• Python 3.9+
• NumPy >= 1.19.0

License

MIT License - see LICENSE file for details.