# ConstrainedDelaunay2D

vtk-examples/Cxx/Filtering/ConstrainedDelaunay2D

### Description¶

Perform a 2D Delaunay triangulation respecting a specified boundary. This examples constructs a 10x10 grid of points. It then defines a polygon that uses the points in the grid. We want to triangulate all of the points except the region inside the boundary of the polygon. We expect a rectangular hole of size 4x3 in the resulting triangulated plane.

Other languages

See (Python)

Question

### Code¶

ConstrainedDelaunay2D.cxx

#include <vtkActor.h>
#include <vtkCellArray.h>
#include <vtkDelaunay2D.h>
#include <vtkMinimalStandardRandomSequence.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkPolygon.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>

int main(int, char*[])
{
vtkNew<vtkNamedColors> colors;

// Generate a 10 x 10 grid of points
vtkNew<vtkPoints> points;
unsigned int gridSize = 10;
unsigned int seed = 0;
vtkNew<vtkMinimalStandardRandomSequence> randomSequence;
randomSequence->Initialize(seed);
for (unsigned int x = 0; x < gridSize; x++)
{
for (unsigned int y = 0; y < gridSize; y++)
{
auto d1 = randomSequence->GetValue() / 2.0 - 0.25;
randomSequence->Next();
auto d2 = randomSequence->GetValue() / 2.0 - 0.25;
randomSequence->Next();
points->InsertNextPoint(x + d1, y + d2, 0);
}
}

vtkNew<vtkPolyData> aPolyData;
aPolyData->SetPoints(points);

// Create a cell array to store the polygon in
vtkNew<vtkCellArray> aCellArray;

// Define a polygonal hole with a clockwise polygon
vtkNew<vtkPolygon> aPolygon;

aPolygon->GetPointIds()->InsertNextId(22);
aPolygon->GetPointIds()->InsertNextId(23);
aPolygon->GetPointIds()->InsertNextId(24);
aPolygon->GetPointIds()->InsertNextId(25);
aPolygon->GetPointIds()->InsertNextId(35);
aPolygon->GetPointIds()->InsertNextId(45);
aPolygon->GetPointIds()->InsertNextId(44);
aPolygon->GetPointIds()->InsertNextId(43);
aPolygon->GetPointIds()->InsertNextId(42);
aPolygon->GetPointIds()->InsertNextId(32);

aCellArray->InsertNextCell(aPolygon);

// Create a polydata to store the boundary. The points must be the
// same as the points we will triangulate.
vtkNew<vtkPolyData> boundary;
boundary->SetPoints(aPolyData->GetPoints());
boundary->SetPolys(aCellArray);

// Triangulate the grid points
vtkNew<vtkDelaunay2D> delaunay;
delaunay->SetInputData(aPolyData);
delaunay->SetSourceData(boundary);

// Visualize
vtkNew<vtkPolyDataMapper> meshMapper;
meshMapper->SetInputConnection(delaunay->GetOutputPort());

vtkNew<vtkActor> meshActor;
meshActor->SetMapper(meshMapper);
meshActor->GetProperty()->EdgeVisibilityOn();
meshActor->GetProperty()->SetEdgeColor(
colors->GetColor3d("Peacock").GetData());
meshActor->GetProperty()->SetInterpolationToFlat();

vtkNew<vtkPolyDataMapper> boundaryMapper;
boundaryMapper->SetInputData(boundary);

vtkNew<vtkActor> boundaryActor;
boundaryActor->SetMapper(boundaryMapper);
boundaryActor->GetProperty()->SetColor(
colors->GetColor3d("Raspberry").GetData());
boundaryActor->GetProperty()->SetLineWidth(3);
boundaryActor->GetProperty()->EdgeVisibilityOn();
boundaryActor->GetProperty()->SetEdgeColor(
colors->GetColor3d("Red").GetData());
boundaryActor->GetProperty()->SetRepresentationToWireframe();

// Create a renderer, render window, and interactor
vtkNew<vtkRenderer> renderer;
vtkNew<vtkRenderWindow> renderWindow;
vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
renderWindowInteractor->SetRenderWindow(renderWindow);

// Add the actor to the scene
renderer->SetBackground(colors->GetColor3d("Mint").GetData());

// Render and interact
renderWindow->SetSize(640, 480);
renderWindow->SetWindowName("ConstrainedDelaunay2D");
renderWindow->Render();
renderWindowInteractor->Start();

return EXIT_SUCCESS;
}


### CMakeLists.txt¶

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(ConstrainedDelaunay2D)

find_package(VTK COMPONENTS
CommonColor
CommonCore
CommonDataModel
FiltersCore
InteractionStyle
RenderingContextOpenGL2
RenderingCore
RenderingFreeType
RenderingGL2PSOpenGL2
RenderingOpenGL2
)

if (NOT VTK_FOUND)
message(FATAL_ERROR "ConstrainedDelaunay2D: Unable to find the VTK build folder.")
endif()

# Prevent a "command line is too long" failure in Windows.
set(CMAKE_NINJA_FORCE_RESPONSE_FILE "ON" CACHE BOOL "Force Ninja to use response files.")
target_link_libraries(ConstrainedDelaunay2D PRIVATE ${VTK_LIBRARIES} ) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS ConstrainedDelaunay2D MODULES${VTK_LIBRARIES}
)


cd ConstrainedDelaunay2D/build


If VTK is installed:

cmake ..


If VTK is not installed but compiled on your system, you will need to specify the path to your VTK build:

cmake -DVTK_DIR:PATH=/home/me/vtk_build ..


Build the project:

make


and run it:

./ConstrainedDelaunay2D


WINDOWS USERS

Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.