vtkbool

About

This is an extension of the graphics library VTK. The goal of the extension is to equip the library with rebust boolean operations on polygonal meshes. I started the project at the end of my studies in mechanical engineering at the University of Applied Sciences (HTWK) in Leipzig. I used VTK to develop a program, which I had to create for a paper. At this time I would have wished, that this feature already exists. There was several implementations from third parties, but after some tests, I came to the conclusion, that none of them worked correct. I decided to start with my own implementation. This library is the result of my efforts.

Features

• based on VTK
• 4 operation types available (union, intersection, difference and difference2 - difference with interchanged operands)
• triangulation is not needed
• all types of polygonal cells are supported (triangles, quads, polygons, triangle-strips)
• triangle-strips and quads will be transformed into triangles (quads only if their points are not on the same plane)
• non-convex polygons are allowed
• meshes can be stacked (coplanar polygons are right handled)
• the meshes don’t need to be watertight
• CellData is passed (attached by the rules of vtkAppendPolyData)
• contact-lines are available in the 3th output
• the filter is able to embed holes
• compileable as ParaView plugin
• Python wrapped

Limitations

• the filter assumes well defined triangles, quads and polygons
• PointData is not preserved - you have to do your own mapping with OrigCellIdsA and OrigCellIdsB

Requirements

• CMake >= 3.12
• VTK >= 9.0
• C++17 compiler

Optional

• ParaView >= 5.0
• Python 3.x

Library

To include vtkbool into your program, you have to compile it as a library. All you need is an installation of VTK with header files. If you have installed VTK over your package manager, CMake is able to find the required files. Otherwise you have to set VTK_DIR manually. It must be a path like /home/zippy/VTK9/lib/cmake/vtk-9.1 or C:/Users/zippy/VTK9/lib/cmake/vtk-9.1.

The usage of the library is very simple. Look at the example in the section below. You can set the operation mode by calling one of the named methods:

• SetOperModeToNone
• SetOperModeToUnion
• SetOperModeToIntersection
• SetOperModeToDifference
• SetOperModeToDifference2

The alternative is the more generic SetOperMode. The method must be called with the number of the desired operation, an integer between 0 and 4, with the same meaning as mentioned before. The default is Union.

C++ Example

Create a directory somewhere in your file system, download vtkbool and unpack it into that.

mkdir example cd example git clone https://github.com/zippy84/vtkbool.git

Then create the following two files:

test.cxx

```C++

include

include

include

include

include "vtkPolyDataBooleanFilter.h"

int main (int argc, char *argv[]) { auto cube = vtkSmartPointer::New(); cube->SetYLength(.5);

auto cyl = vtkSmartPointer<vtkCylinderSource>::New();
cyl->SetResolution(32);
cyl->SetHeight(.5);
cyl->SetCenter(0, .5, 0);

auto bf = vtkSmartPointer<vtkPolyDataBooleanFilter>::New();
bf->SetInputConnection(0, cube->GetOutputPort());
bf->SetInputConnection(1, cyl->GetOutputPort());
bf->SetOperModeToDifference();

auto writer = vtkSmartPointer<vtkPolyDataWriter>::New();
writer->SetInputConnection(bf->GetOutputPort());
writer->SetFileName("result.vtk");
writer->Update();

return 0;

} ```

CMakeLists.txt

```CMake cmakeminimumrequired(VERSION 3.12 FATAL_ERROR) project(test)

set(CMAKECXXSTANDARD 17) set(CMAKECXXSTANDARD_REQUIRED ON)

find_package(VTK REQUIRED COMPONENTS FiltersSources IOLegacy)

find_package(VTK REQUIRED COMPONENTS FiltersSources IOLegacy FiltersExtraction FiltersGeometry FiltersModeling FiltersFlowPaths WrappingPythonCore)

if(VTKFOUND) includedirectories(vtkbool) add_subdirectory(vtkbool)

add_executable(test test.cxx)
target_link_libraries(test PRIVATE vtkbool ${VTK_LIBRARIES})

vtk_module_autoinit(
    TARGETS test
    MODULES ${VTK_LIBRARIES}
)

endif(VTK_FOUND) ```

Inside the example directory, create a subdirectory called build and cd into it. You should have a directory structure that looks something like this:

example ├── build ├── CMakeLists.txt ├── test.cxx └── vtkbool ├── CMakeLists.txt ├── ... └── vtkPolyDataBooleanFilter.h

From inside the build directory, run ccmake .., follow the instructions, and finally type make.

Running ./test will now produce the result.vtk file.

ParaView Plugin

To build the plugin you have to compile ParaView from source. Download the current version from http://www.paraview.org and follow the compilation instructions. As soon as ParaView is compiled, it may take a while, you can build the plugin by activating the VTKBOOL_PARAVIEW option within CMake. In CMake you also have to point to ParaView_DIR if CMake can't found it and it is not installed in a common location like /usr/lib or /usr/local/lib. Make sure PARAVIEWINSTALLDEVELOPMENT_FILES is set.

When everything has been compiled successfully, you can install the plugin.

Python

The Python module will be generated automatically, if three conditions are met:

• vtkbool is configured as a library
• Python 3 is installed with header files
• VTK itself is wrapped to Python

After a successful compilation, the module can be used as follows:

```python

!/usr/bin/env python

import sys sys.path.append('/path/to/your/build/directory') # also look into the python files in the testing directory

from vtkmodules.vtkFiltersSources import vtkCubeSource, vtkSphereSource from vtkmodules.vtkIOLegacy import vtkPolyDataWriter from vtkbool import vtkPolyDataBooleanFilter

cube = vtkCubeSource()

sphere = vtkSphereSource() sphere.SetCenter(.5, .5, .5) sphere.SetThetaResolution(20) sphere.SetPhiResolution(20)

bf = vtkPolyDataBooleanFilter() bf.SetInputConnection(0, cube.GetOutputPort()) bf.SetInputConnection(1, sphere.GetOutputPort()) bf.SetOperModeToDifference()

write the result, if you want ...

writer = vtkPolyDataWriter() writer.SetInputConnection(bf.GetOutputPort()) writer.SetFileName('result.vtk')

writer.Update() ```

Or with VTK >= 9.4:

```python

!/usr/bin/env python

import sys sys.path.append('/path/to/your/build/directory')

from vtkmodules.vtkFiltersSources import vtkCubeSource, vtkSphereSource from vtkmodules.vtkIOLegacy import vtkPolyDataWriter from vtkmodules.util.executionmodel import selectports

from vtkbool import vtkPolyDataBooleanFilter, OPER_DIFFERENCE

cube = vtkCubeSource() sphere = vtkSphereSource(center=[.5, .5, .5], thetaresolution=20, phiresolution=20)

bf = vtkPolyDataBooleanFilter(opermode=OPERDIFFERENCE) cube >> bf sphere >> select_ports(1, bf)

(bf >> vtkPolyDataWriter(file_name='result.vtk')).update()

```

Conda

The library is also available at conda-forge. In your virtual environment you can install the package with:

conda install -c conda-forge vtkbool

Unlike in the python example, you need to import it like this:

python from vtkbool.vtkbool import vtkPolyDataBooleanFilter

Errors and their meaning

• Contact failed with ...

  • Found invalid intersection points.

  This problem occurs when an intersection point is located on congruent edges of a self-intersecting polygon. - Intersection points do not lie on the edges (cells a, b).

  At least one intersection point does not lie on the boundary of the intersected polygon. The points of the polygon do not lie on a plane. The polygon is degenerated. - Intersection goes through non-manifold edges.

  Non-manifold edges are generally not a problem. Unless they are part of the intersection.

• Cannot prevent equal capture points.

A capture point is the projection of a point onto one of the edges of the intersected polygon. This point, not the projection, is usually used by two lines that are assigned to the two adjacent polygons, sharing this edge. There is a case where two different points have the same projection. The error occurs when the problem could not be solved.

• There is no contact.

What it says.

• At least one line-end has only one neighbor.

The intersection is incomplete. Therefore the cell cannot be divided.

• Strips are invalid.

There are intersection lines that intersect themselves. Either one of the inputs contains an assembly or there is one self-intersecting polygon that is involved in the intersection.

• CutCells failed.

Will be printed out only, if some holes couldn't be merged into their outer polygons.

• Boolean operation failed.

A boolean operation can fail at the end, if some of the intersection lines are not part of the result.

Copyright

2012-2025 Ronald Römer

License

Apache License, Version 2.0