# Using Gradient Filter

**URL:** https://discourse.vtk.org/t/using-gradient-filter/2734
**Category:** Support
**Created:** [March 2, 2020, 2:56pm UTC](https://discourse.vtk.org/t/using-gradient-filter/2734 "2020-03-02T14:56:12Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![ShaneKirkbride](https://discourse.vtk.org/user_avatar/discourse.vtk.org/shanekirkbride/32/1392_2.png) [@ShaneKirkbride](https://discourse.vtk.org/u/ShaneKirkbride)
#### Post date: [March 2, 2020, 2:56pm UTC](https://discourse.vtk.org/t/using-gradient-filter/2734/1 "2020-03-02T14:56:12Z")

</div>

I’m trying to use the GradentFilter example:  
[https://vtk.org/Wiki/VTK/Examples/Cxx/PolyData/GradientFilter](https://vtk.org/Wiki/VTK/Examples/Cxx/PolyData/GradientFilter)

I can’t get my mesh to show the color changes the way the one in the picture shows. Is there some example data I can look at? I’d like to colorize my gradients.

Here is what I’m doing:

```
#include <string>
#include <vtkSmartPointer.h>
#include <vtkMarchingCubes.h>
#include <vtkVoxelModeller.h>
#include <vtkSphereSource.h>
#include <vtkImageData.h>
#include <vtkDICOMImageReader.h>
#include <vtkJPEGReader.h>
#include <vtkActor.h>
#include <vtkPolyDataMapper.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkImageViewer2.h>

#include <vtkSmartPointer.h>

#include <vtkActor.h>
#include <vtkArrowSource.h>
#include <vtkAssignAttribute.h>
#include <vtkCamera.h>
#include <vtkExtractEdges.h>
#include <vtkGlyph3D.h>
#include <vtkGradientFilter.h>
#include <vtkPolyDataMapper.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkTubeFilter.h>
#include <vtkUnstructuredGridReader.h>

using namespace std;
int main(int argc, char *argv[])
{
  vtkSmartPointer<vtkImageData> volume =
    vtkSmartPointer<vtkImageData>::New();
  double isoValue;
   
    vtkSmartPointer<vtkDICOMImageReader> reader = vtkSmartPointer<vtkDICOMImageReader>::New();
    reader->SetDirectoryName(argv[1]);
    reader->Update();
    volume->DeepCopy(reader->GetOutput());
    isoValue = atof(argv[2]);
    
    std::string inputFilename = argv[1];
    vtkSmartPointer<vtkMarchingCubes> surface =
        vtkSmartPointer<vtkMarchingCubes>::New();
    surface->SetInputData(volume);
    surface->ComputeNormalsOn();
    surface->SetValue(0, isoValue);

    // Create polydata from iso-surface
    vtkSmartPointer<vtkPolyData> marched = vtkSmartPointer<vtkPolyData>::New();
    surface->Update();
    marched->DeepCopy(surface->GetOutput());
    std::cout << "Number of points: " << marched->GetNumberOfPoints() << std::endl;
         
  vtkSmartPointer<vtkExtractEdges> edges = vtkSmartPointer<vtkExtractEdges>::New();
  edges->SetInputData(marched); // ->SetInputData(outputMesh); // ->SetInputConnection(reader->GetOutputPort());

  vtkSmartPointer<vtkTubeFilter> tubes = vtkSmartPointer<vtkTubeFilter>::New();
  tubes->SetInputConnection(edges->GetOutputPort());
  tubes->SetRadius(0.01);
  tubes->SetVaryRadiusToVaryRadiusOff();
  tubes->SetNumberOfSides(4);

  vtkSmartPointer<vtkPolyDataMapper> tubesMapper = vtkSmartPointer<vtkPolyDataMapper>::New();
  tubesMapper->SetInputConnection(tubes->GetOutputPort());
  tubesMapper->SetScalarRange(0.0, 25.0);

  vtkSmartPointer<vtkActor> tubesActor = vtkSmartPointer<vtkActor>::New();
  tubesActor->SetMapper(tubesMapper);

  vtkSmartPointer<vtkGradientFilter> gradients = vtkSmartPointer<vtkGradientFilter>::New();
  gradients->SetInputData(marched); // ->SetInputConnection(reader->GetOutputPort());

  vtkSmartPointer<vtkAssignAttribute> vectors = vtkSmartPointer<vtkAssignAttribute>::New();
  vectors->SetInputConnection(gradients->GetOutputPort());
  vectors->Assign("Gradients", vtkDataSetAttributes::VECTORS, vtkAssignAttribute::POINT_DATA);

  vtkSmartPointer<vtkArrowSource> arrow = vtkSmartPointer<vtkArrowSource>::New();

  vtkSmartPointer<vtkGlyph3D> glyphs = vtkSmartPointer<vtkGlyph3D>::New();
  glyphs->SetInputConnection(0, vectors->GetOutputPort());
  glyphs->SetInputConnection(1, arrow->GetOutputPort());
  glyphs->ScalingOn();
  glyphs->SetScaleModeToScaleByVector();
  glyphs->SetScaleFactor(0.25);
  glyphs->OrientOn();
  glyphs->ClampingOff();
  glyphs->SetVectorModeToUseVector();
  glyphs->SetIndexModeToOff();

  vtkSmartPointer<vtkPolyDataMapper> glyphMapper = vtkSmartPointer<vtkPolyDataMapper>::New();
  glyphMapper->SetInputConnection(glyphs->GetOutputPort());
  glyphMapper->ScalarVisibilityOff();

  vtkSmartPointer<vtkActor> glyphActor = vtkSmartPointer<vtkActor>::New();
  glyphActor->SetMapper(glyphMapper);

  vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
  renderer->AddActor(tubesActor);
  renderer->AddActor(glyphActor);
  renderer->SetBackground(0.328125, 0.347656, 0.425781);

  vtkSmartPointer<vtkRenderWindow> renwin =
      vtkSmartPointer<vtkRenderWindow>::New();
  renwin->AddRenderer(renderer);
  renwin->SetSize(600, 600);

  renderer->ResetCamera();
  vtkCamera* camera = renderer->GetActiveCamera();
  camera->Elevation(-80.0);
  camera->OrthogonalizeViewUp();
  camera->Azimuth(135.0);

  vtkSmartPointer<vtkRenderWindowInteractor> iren =
      vtkSmartPointer<vtkRenderWindowInteractor>::New();
  iren->SetRenderWindow(renwin);
  renwin->Render();
  iren->Initialize();
  iren->Start();

  return EXIT_SUCCESS;
}

```

Here is the result:

 ![image](https://discourse.vtk.org/uploads/default/original/2X/d/d066033d9a8ec182b1daf07618dbe1899c116f07.png)

---

<div class="post-metadata">

### Author: ![amaclean](https://discourse.vtk.org/user_avatar/discourse.vtk.org/amaclean/32/224_2.png) [@amaclean](https://discourse.vtk.org/u/amaclean)
#### Post date: [March 3, 2020, 4:18am UTC](https://discourse.vtk.org/t/using-gradient-filter/2734/2 "2020-03-03T04:18:33Z")

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This is the most recent version of [GradientFilter](https://lorensen.github.io/VTKExamples/site/Cxx/PolyData/GradientFilter/). The data file used in this example is `VTKExamples/src/Testing/Data/uGridEx.vtk`, if you haven’t already downloaded the VTKExamples, the instructions for doing this can be found on the [VTKExamples](https://lorensen.github.io/VTKExamples/site/) site.