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List:       vtkusers
Subject:    Re: [vtkusers] How do I display a scalar field over a rectilinear
From:       David Doria <daviddoria+vtk () gmail ! com>
Date:       2010-02-16 13:08:26
Message-ID: c19fcadc1002160508h1e1fed92y14c3707a491ea79d () mail ! gmail ! com
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On Mon, Feb 15, 2010 at 9:02 PM, Roland Krause <rokrau@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
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