[vtkusers] How do I display a scalar field over a rectilinear grid using colors

[David Doria]

On Mon, Feb 15, 2010 at 9:02 PM, Roland Krause <rokrau at yahoo.com> wrote:
> Hi all, I am relatively new to Vtk and have a rather basic question.
>
> I am trying to display a colored iso-surface plot of an array of scalar values given at the points of a rectangular grid.
>
> Below is my code, the result of which is a white plane with the geometry of the object (it is a 2D grid) I am trying to visualize. My basic question is of course : What's wrong? What am I missing? Is there a basic example of how this should be done?
>
> My understanding is that I make vtkPolyData out of the vtkRectilinearGrid using the filter, then add the scalar array I am trying to plot over the grid as a vtkDataArray to the vtkPointData of this vtkPolyData. Finally assign it to be recognized as POINT_DATA and then plot the thing using the default lookup table (which also looks really wrong btw.)
>
> Vector<T> is a simple Vector class that has a T * operator() - and a size() function, nothing too special...
>
> void SnapshotView2D::plot(const Vector<float> & xc, const Vector<float> & yc, const Vector<float> & zc, const Vector<float> & data)
> {
>    const int n1=xc.size(), n2=yc.size(), n3=zc.size();
>
>    vtkSmartPointer<vtkFloatArray> xCoords = vtkFloatArray::New();
>    xCoords->SetArray(const_cast<Vector<float>&>(xc),xc.size(),1);
>
>    vtkSmartPointer<vtkFloatArray> yCoords = vtkFloatArray::New();
>    yCoords->SetArray(const_cast<Vector<float>&>(yc),yc.size(),1);
>
>    vtkSmartPointer<vtkFloatArray> zCoords = vtkFloatArray::New();
>    zCoords->SetArray(const_cast<Vector<float>&>(zc),zc.size(),1);
>
>    vtkSmartPointer<vtkFloatArray> scalars = vtkFloatArray::New();
>    scalars->SetArray(const_cast<Vector<float>&>(data),data.size(),1);
>    scalars->SetName("scalars");
>
>    vtkSmartPointer<vtkRectilinearGrid> rgrid = vtkRectilinearGrid::New();
>    rgrid->SetDimensions(n1,n2,n3);
>    rgrid->SetXCoordinates(xCoords);
>    rgrid->SetYCoordinates(yCoords);
>    rgrid->SetZCoordinates(zCoords);
>
>    plane = vtkRectilinearGridGeometryFilter::New();
>    plane->SetInput(rgrid);
>    plane->SetExtent(0,n1-1,0,n2-1, 0,n3-1);
>
>    vtkPolyData * planeData = plane->GetOutput();
>    vtkPointData * pointData = planeData->GetPointData();
>    pointData ->AddArray(scalars);
>
>    vtkAssignAttribute * assign = vtkAssignAttribute::New();
>    assign->SetInput(planeData);
>    assign->Assign("scalars", vtkDataSetAttributes::SCALARS, vtkAssignAttribute::POINT_DATA);
>    assign->Update();
>
>    vtkSmartPointer<vtkLookupTable> pLookupTable = vtkSmartPointer<vtkLookupTable>::New();
> //    pLookupTable->SetTableRange(planeData->GetScalarRange());
>    pLookupTable->SetNumberOfTableValues(10);
> //    pLookupTable->SetHueRange(0.667,0.0);
> //    pLookupTable->SetValueRange(0.0,1.0);
>
>    pMapper = vtkPolyDataMapper::New();
>    pMapper->SetInput(planeData);
>    pMapper->ImmediateModeRenderingOn();
>    pMapper->ScalarVisibilityOn();
>    pMapper->SetScalarModeToUsePointData();
>    pMapper->SetScalarRange(planeData->GetScalarRange());
>
>    pMapper->SetLookupTable(pLookupTable);
>
>    // Create a scalar bar
>    vtkScalarBarActor * scalarBar = vtkScalarBarActor::New();
>    scalarBar->SetLookupTable(pLookupTable);
> //     scalarBar SetTitle "Temperature"
> //     [scalarBar GetPositionCoordinate] SetCoordinateSystemToNormalizedViewport
> //     [scalarBar GetPositionCoordinate] SetValue 0.1 0.01
> //     scalarBar SetOrientationToHorizontal
> //     scalarBar SetWidth 0.8
> //     scalarBar SetHeight 0.17
>
>    pActor = vtkActor::New();
>    pActor->SetMapper(pMapper);
> //    pActor->GetProperty()->SetRepresentationToWireframe();
> //    pActor->GetProperty()->SetColor(0,0,0);
>
>    pRenderer->AddActor(scalarBar);
>    pRenderer->AddActor(pActor);
>    pRenderer->SetBackground(1,1,1);
>    pRenderer->ResetCamera();
>
>    pRenderWindow->Render();
>    pRenderer->SetBackground(0.9,0.9,0.9); // Background color white
>
>    vtkAxesActor * pAxes = vtkAxesActor::New();
>    vtkOrientationMarkerWidget * pWidget = vtkOrientationMarkerWidget::New();
>    pWidget->SetOutlineColor( 0.9300, 0.5700, 0.1300 );
>    pWidget->SetOrientationMarker( pAxes );
>    pWidget->SetInteractor(pRenderWindowInteractor);
>    pWidget->InteractiveOff();
>
>    // Reset camera
>    pRenderer->ResetCamera();
>    pRenderWindow->Render();
>
>    pWidget->SetEnabled( 1 );
>    pRenderWindowInteractor->Start();
> }
>
> I would be greatful if you could point me to an example, I had assumed that this is one of the most basic things one could do in Vtk.
>
> Best regards and many thanks
> Roland

This :
vtkSmartPointer<vtkFloatArray> xCoords = vtkFloatArray::New();

is very bad - the reference count (the whole thing that makes smart
pointers work) will be off unless you use:

vtkSmartPointer<vtkFloatArray> xCoords = vtkSmartPointer<vtkFloatArray>::New();

on all of your smart pointer initializations.

Take a look at this:
http://www.vtk.org/Wiki/VTK/Tutorials/SmartPointers

To get to your real question:

This example:
http://www.vtk.org/Wiki/VTK/Examples/Color_a_mesh_by_height

demonstrates how to color a PolyData. I've never used
vtkRectilinearGrid, but I believe the process should be identical.
Take a look at that example and see if it helps at all - if not, let
us know and we'll take a closer look.

Thanks,

David