# Recoloring

**URL:** https://discourse.vtk.org/t/recoloring/1951
**Category:** Support
**Created:** [October 20, 2019, 3:14am UTC](https://discourse.vtk.org/t/recoloring/1951 "2019-10-20T03:14:25Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![gib](https://discourse.vtk.org/user_avatar/discourse.vtk.org/gib/32/9201_2.png) [@gib](https://discourse.vtk.org/u/gib)
#### Post date: [October 20, 2019, 3:14am UTC](https://discourse.vtk.org/t/recoloring/1951/1 "2019-10-20T03:14:25Z")

</div>

Starting from a set of 3D points, I generate a 2D triangular unstructured grid in a vtkPolyData and use the z values to assign colors to the points, using a vtkLookupTable. The vtkPolyData is then rendered as a surface. This all works fine. I want to be able to change the color lookup table to recolor the rendered surface. So far my attempts to do this have not been successful. Here is the code (points is a vtkPoints object that has been populated with npts 3D points.)

```
vtkPolyData *inputPolyData = vtkPolyData::New();
inputPolyData->SetPoints(points);

```

// Triangulate the grid points  
vtkDelaunay2D \*delaunay = vtkDelaunay2D::New();

#if VTK\_MAJOR\_VERSION\_5  
delaunay-\>SetInput(inputPolyData);  
#else  
delaunay-\>SetInputData(inputPolyData);  
#endif

```
delaunay->Update();
vtkPolyData *outputPolyData = delaunay->GetOutput();
double minz, maxz;
double *colarray = new double[npts];
 minz = 0;
 maxz = 0.18;

```

// Create the color map  
vtkLookupTable \*colorLookupTable = vtkLookupTable::New();  
colorLookupTable-\>SetTableRange(minz, maxz);  
colorLookupTable-\>Build();  
// Generate the colors for each point based on the color map  
vtkUnsignedCharArray \*colors = vtkUnsignedCharArray::New();  
colors-\>SetNumberOfComponents(3);  
// Create a mapper and actor  
vtkPolyDataMapper \*mapper = vtkPolyDataMapper::New();  
vtkActor \*actor = vtkActor::New();  
actor-\>SetMapper(mapper);  
int npts = outputPolyData-\>GetNumberOfPoints();  
for (int i = 0; i \< npts; i++) {  
double \*p = outputPolyData-\>GetPoint(i);  
colarray[i] = p[2];  
double dcolor[3];  
colorLookupTable-\>GetColor(colarray[i],dcolor);  
unsigned char \*color = new unsigned char[3];  
for (int j = 0; j \< 3; j++) {  
color[j] = (unsigned char)( 255 \* dcolor[j] );  
}  
colors-\>InsertNextTuple3(color[0], color[1], color[2] );  
}  
outputPolyData-\>GetPointData()-\>SetScalars(colors);

#if VTK\_MAJOR\_VERSION\_5  
mapper-\>SetInputConnection(outputPolyData-\>GetProducerPort());  
#else  
mapper.SetInputData(outputPolyData);  
#endif

```
vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
vtkSmartPointer<vtkRenderWindow> renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
renderWindow->AddRenderer(renderer);
renderWindow->SetSize(640,640);
vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor = 
  vtkSmartPointer<vtkRenderWindowInteractor>::New();
renderWindowInteractor->SetRenderWindow(renderWindow);

```

// Add the actor to the scene  
renderer-\>AddActor(actor);  
renderer-\>SetBackground(.1, .3,.2); // Background color dark green  
// Render and interact  
renderWindow-\>Render();  
renderWindowInteractor-\>Start();

// Try changing the colours  
minz = 0.99\*maxz;  
colorLookupTable-\>SetTableRange(minz, maxz);  
colorLookupTable-\>Build();  
colors-\>Reset();  
for (int i = 0; i \< npts; i++) {  
double dcolor[3];  
colorLookupTable-\>GetColor(colarray[i],dcolor);  
unsigned char \*color = new unsigned char[3];  
for (int j = 0; j \< 3; j++) {  
color[j] = (unsigned char)( 255 \* dcolor[j] );  
}  
colors-\>InsertNextTuple3(color[0], color[1], color[2] );  
}

```
outputPolyData->GetPointData()->SetScalars(colors);
outputPolyData->Update();
mapper->Update();
renderWindow->Render();
return;

```

The code after “// Try changing the colours” has no effect on what is displayed. (If I put “minz = 0.99\*maxz” after the line “maxz = 0.18” I get a very different coloring from the initial render.)

What am I doing wrong?