# BIMShellExtractor

**Repository Path**: zhoulch/bimshell-extractor

## Basic Information

- **Project Name**: BIMShellExtractor
- **Description**: No description available
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2026-01-20
- **Last Updated**: 2026-01-21

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# BIM Shell Extractor

This repository provides a **public, research-oriented implementation** of a voxel-based method for extracting **external shell components** from BIM-derived geometry.

The code is released to support **algorithmic transparency and architectural-level reproducibility**, in response to reviewer and editor requests.

Due to funding and intellectual property constraints, this repository contains a **simplified public version** of the original implementation. Core data structures and processing logic are preserved, while selected geometric predicates and engineering optimizations are replaced with baseline implementations.

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## 1. Method Overview

The implemented workflow consists of four main stages:

1. **Geometry abstraction**
   BIM components are represented as lightweight geometric entities with vertices, indices, and axis-aligned bounding boxes.

2. **Voxel grid construction**
   A uniform 3D voxel grid is built over the global bounding box of the scene.

3. **Voxel-based spatial classification**
   Grid cells are classified as `Occupied`, `Outside`, `Indoor`, or `Shell` based on connectivity and neighborhood relationships.

4. **External shell identification**
   Components occupying at least one `Shell` voxel are identified as external shell components.

The public release focuses on **component-level shell extraction**, which corresponds to the core method described in the paper.

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## 2. Repository Structure

src/
├─ functions/
│ ├─ BimEntityShape3D.hpp
│ ├─ TriangleFace.hpp
│ ├─ BimGrid.hpp
│ ├─ BimShellExtractor.hpp
│ ├─ BimShellExtractorPipeline.hpp
│ ├─ BimShellExtractorIO.hpp
│ ├─ BimShellTopology.hpp
│ ├─ BimShellFaceExtraction.hpp
│ └─ MeshVertexDedup.hpp
└─ demo/

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## 3. Public Release Scope

### Included
- Complete end-to-end pipeline for external shell extraction
- Voxel-based spatial reasoning logic
- Clear data structures and module interfaces
- Runnable example using simplified geometry input
- Export for result inspection

### Simplified or Abstracted
The following aspects are **intentionally simplified** in the public release:

- Exact triangle–voxel and ray–triangle intersection tests
- Topology-aware mesh reconstruction and coplanar face merging
- Robust geometric predicates and performance-oriented optimizations
- Multi-threading and engineering-level acceleration strategies

These components are replaced with **baseline or placeholder implementations** that preserve algorithmic structure without exposing internal project details.

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## 4. Dependencies
- C++17 compatible compiler
- Eigen (required)

Optional (disabled by default):
- IFC parsing libraries and advanced geometry toolkits

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## 5. Configuration

Key parameters are exposed via `BimShellExtractor::Config`, including:

- `cellSize`: voxel resolution
- `tolerance`: geometric tolerance
- Optional flags for IFC I/O, topology reconstruction, and face-level processing

Changing `cellSize` affects both detection granularity and runtime.

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## 6. Reproducibility Notes

- The public release guarantees **structural reproducibility** of the algorithmic workflow.
- Numerical and geometric results may differ from the internal version due to simplified predicates.
- Baseline modules may be replaced with higher-fidelity implementations, provided interfaces are preserved.

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## 7. Intended Use

This repository is intended for:

- Methodological inspection during peer review
- Understanding the algorithmic framework of voxel-based shell extraction
- Serving as a reference implementation for further research

It is **not intended as a production-ready BIM processing system**.