The Problem with Boolean Difference

Oct 13, 2025 by wbrum.org 95 views

Introduction

When working with polygon meshes, boolean operations are a common technique used to combine or subtract shapes. However, these operations can sometimes produce meshes with a large number of triangles, which can be computationally expensive and visually unappealing. In this article, we will explore the process of cleaning up meshes after boolean difference using two methods: brep conversion and corefinement.

What is Boolean Difference?

Boolean difference is a mathematical operation that takes two shapes as input and produces a new shape that represents the difference between the two input shapes. In the context of polygon meshes, this operation is used to subtract one shape from another, resulting in a new mesh that represents the remaining shape.

The Problem with Boolean Difference

While boolean difference is a powerful tool for mesh manipulation, it can sometimes produce meshes with a large number of triangles. This is because the operation can create new triangles at the boundary between the two input shapes, resulting in a mesh with a high degree of complexity.

Method 1: Brep Conversion

One way to clean up meshes after boolean difference is to use the brep conversion method. Brep stands for boundary representation, which is a data structure used to represent the boundary of a shape. The brep conversion method involves converting the mesh into a brep representation and then using algorithms to simplify the brep representation.

How Brep Conversion Works

The brep conversion method works by first converting the mesh into a brep representation. This involves identifying the boundary edges of the mesh and creating a new data structure that represents the boundary of the shape. The brep representation is then simplified using algorithms such as edge collapse or vertex removal.

Example Code: Brep Conversion

Here is an example code snippet that demonstrates how to use the brep conversion method to clean up a mesh after boolean difference:

#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Polygon_mesh_processing/corefinement.h>
#include <CGAL/Polygon_mesh_processing/brep_conversion.h>

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Polygon_mesh_traits_3<K> Traits;

int main() {
  // Create a polygon mesh
  Traits::Polygon_mesh mesh;

  // Perform boolean difference
  CGAL::Polygon_mesh_processing::corefinement_difference_remeshed(mesh, mesh);

  // Convert mesh to brep representation
  CGAL::Polygon_mesh_processing::brep_conversion(mesh);

  // Simplify brep representation
  CGAL::Polygon_mesh_processing::simplify_brep(mesh);

  return 0;
}

Method 2: Corefinement

Another way to clean up meshes after boolean difference is to use the corefinement method. Corefinement is a technique used to simplify a mesh by removing unnecessary triangles and edges.

How Corefinement Works

The corefinement method works by first identifying the unnecessary triangles and edges in the mesh. These triangles and edges are then removed, resulting in a simplified mesh.

Example Code: Corefinement

Here is an example code snippet that demonstrates how to use the corefinement method to clean up a mesh after boolean difference:

#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Polygon_mesh_processing/corefinement.h>

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Polygon_mesh_traits_3<K> Traits;

int main() {
  // Create a polygon mesh
  Traits::Polygon_mesh mesh;

  // Perform boolean difference
  CGAL::Polygon_mesh_processing::corefinement_difference_remeshed(mesh, mesh);

  // Simplify mesh using corefinement
  CGAL::Polygon_mesh_processing::corefinement_simplify(mesh);

  return 0;
}

Conclusion

In this article, we have explored two methods for cleaning up meshes after boolean difference: brep conversion and corefinement. Both methods can be used to simplify a mesh and reduce the number of triangles, resulting in a more efficient and visually appealing mesh. By using these methods, developers can create more complex and realistic models while minimizing the computational cost.

Future Work

In the future, we plan to explore other methods for cleaning up meshes after boolean difference, such as using mesh decimation or mesh smoothing algorithms. We also plan to investigate the use of these methods in real-world applications, such as computer-aided design (CAD) and computer-aided manufacturing (CAM).

References

CGAL: Polygon Mesh Processing. https://doc.cgal.org/latest/Polygon_mesh_processing/index.html
CGAL: Brep Conversion. https://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2brep_conversion_8cpp-example.html
CGAL: Corefinement. https://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2corefinement_difference_remeshed_8cpp-example.html
Clean Up Meshes after Boolean Difference: A Q&A Guide ===========================================================

Introduction

In our previous article, we explored two methods for cleaning up meshes after boolean difference: brep conversion and corefinement. In this article, we will answer some frequently asked questions (FAQs) about these methods and provide additional information to help developers understand how to use them effectively.

Q: What is the difference between brep conversion and corefinement?

A: Brep conversion and corefinement are two different methods for cleaning up meshes after boolean difference. Brep conversion involves converting the mesh into a brep representation and then simplifying it using algorithms such as edge collapse or vertex removal. Corefinement, on the other hand, involves identifying and removing unnecessary triangles and edges in the mesh.

Q: Which method is more efficient?

A: The efficiency of the two methods depends on the specific use case and the complexity of the mesh. Brep conversion can be more efficient for meshes with a high degree of complexity, as it can simplify the mesh by removing unnecessary triangles and edges. Corefinement, on the other hand, can be more efficient for meshes with a simpler structure, as it can remove unnecessary triangles and edges more quickly.

Q: Can I use both methods together?

A: Yes, you can use both methods together to clean up a mesh after boolean difference. This can be useful if you need to simplify a mesh with a high degree of complexity, as brep conversion can be used to simplify the mesh, and then corefinement can be used to further simplify the mesh.

Q: How do I choose the right method for my use case?

A: To choose the right method for your use case, you should consider the following factors:

The complexity of the mesh: If the mesh has a high degree of complexity, brep conversion may be a better choice. If the mesh has a simpler structure, corefinement may be a better choice.
The desired level of simplification: If you need to simplify the mesh by a large amount, brep conversion may be a better choice. If you need to simplify the mesh by a small amount, corefinement may be a better choice.
The computational resources available: If you have limited computational resources, corefinement may be a better choice, as it can be more efficient than brep conversion.

Q: Can I use these methods with other mesh processing algorithms?

A: Yes, you can use these methods with other mesh processing algorithms, such as mesh decimation or mesh smoothing. Brep conversion and corefinement can be used as a preprocessing step to simplify the mesh before applying other mesh processing algorithms.

Q: Are there any limitations to these methods?

A: Yes, there are some limitations to these methods. Brep conversion can be computationally expensive for large meshes, and corefinement can be sensitive to the quality of the input mesh. Additionally, both methods may not always produce the desired level of simplification, and may require manual tuning of parameters to achieve the desired result.

Q: Where can I find more information about these methods?

A: You can find more information about these methods in the CGAL documentation, which provides detailed information about the brep conversion and corefinement algorithms, as well as examples and tutorials to help you get started.

Conclusion

In this article, we have answered some frequently asked questions about brep conversion and corefinement, two methods for cleaning up meshes after boolean difference. We hope that this information has been helpful in understanding how to use these methods effectively, and we encourage you to explore the CGAL documentation for more information.

Future Work

References

CGAL: Polygon Mesh Processing. https://doc.cgal.org/latest/Polygon_mesh_processing/index.html
CGAL: Brep Conversion. https://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2brep_conversion_8cpp-example.html
CGAL: Corefinement. https://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2corefinement_difference_remeshed_8cpp-example.html