This is an extension of the graphics library VTK. The goal of the extension is to equip the library with 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.

• 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

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

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

• ParaView >= 5.0
• Python 3.x

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.

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

#include <vtkSmartPointer.h>
#include <vtkCubeSource.h>
#include <vtkCylinderSource.h>
#include <vtkPolyDataWriter.h>

#include "vtkPolyDataBooleanFilter.h"

int main (int argc, char *argv[]) {
    auto cube = vtkSmartPointer<vtkCubeSource>::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_minimum_required(VERSION 3.12 FATAL_ERROR)
project(test)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

# find_package(VTK REQUIRED COMPONENTS FiltersSources IOLegacy)

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

if(VTK_FOUND)
    include_directories(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
    ├── ...
    └── vtkPolyDataContactFilter.h

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

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

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 PARAVIEW_INSTALL_DEVELOPMENT_FILES is set.

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

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:

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)

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

# write the result, if you want ...

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

writer.Update()

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:

from vtkbool.vtkBool import vtkPolyDataBooleanFilter

• Bad shaped cells detected.

  At least one cell has a bad shape. For a cell with more than three points: not all points lie on the plane defined by the calculated surface normal.

• First/Second input has non-manifold edges.

  The contact goes through a non-manifold edge. A non-manifold edge is an edge that is shared by three or more cells. In general this is not a problem, unless they are part of the intersection.

• There is no contact.

  What it says.

• Contact ends suddenly.

  The intersection is incomplete. That is, an intersection line ends in the middle of a cell. The cell cannot be divided.

• Strips are invalid.

  There are two reasons for that kind of error:

  1. at least two intersection lines intersect each other - the input, one of them, contains an assembly
  2. there are different intersection points with the same capturing point - normally a capturing point will be used by only one point of the intersection lines

• CutCells failed.

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

• Boolean operation failed.

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

2012-2024 Ronald Römer

Apache License, Version 2.0