[vtkusers] WarpScalar with an StructuredGrid and Scalar Values - How?

[Bryn Lloyd]

 From the example/test (here C++):
http://public.kitware.com/cgi-bin/viewcvs.cgi/*checkout*/Graphics/Testing/Cxx/expCos.cxx?root=VTK&content-type=text/plain

   // warp plane
   vtkWarpScalar *warp = vtkWarpScalar::New();
   warp->SetInput(xyGrid);
   warp->XYPlaneOn();
   warp->SetScaleFactor(0.5); // depends on your data

   vtkDataSetMapper *map_xyGrid = vtkDataSetMapper::New();
   map_xyGrid->SetInput(warp->GetOutput());


You should not have to do anything with vtkAlgorithm. vtkWarpScalar is a 
algorithm, specifically a pointset algorithm. Since vtkStructuredGrid is 
a vtkPointSet you can use vtkWarpScalar on it.

You could also play with this filter in paraview (www.paraview.org), in 
order to see what it should/will look like if you set up the pipeline 
correctly.

/Bryn



Simon Clift wrote:
> Hi folks,
> 
> I'm new to VTK (but not visualization, used mostly OpenDX, AVS in the past) 
> and I'm having a terrible time with a simple case that I think vtkWarpScalar 
> should solve for me.  I've been through the examples, but none of them seem to 
> apply exactly to my case and I was wondering if the users list might have some 
> insights, please.
> 
> I have a vtkStructuredGrid with dimensions (N_x, N_y, 1 ) and the points are 
> set, but the data is 2D and the z-axis is 0 on all points.   I would like to 
> visualize one of several vtkDoubleArray() values over the same grid with the 
> values specifying the z-distance from the grid.  The grid and the points are 
> generated internally in the program and are not loaded from a file (they will 
> eventually show up in a GUI).
> 
> If I visualize this (for example in my Python code):
> 
>    self.xyGrid = vtk.vtkStructuredGrid()
>    self.xyGrid.SetDimensions( gDim )
>    self.xyGrid.SetInput( pts )   # pts is an N_x*N_y vtkPoints
>    ...
>    self.xyGrid.GetPointData().SetScalars( self.value_1 )
>    self.map_xyGrid = vtk.vtkDataSetMapper()
>    self.map_xyGrid.SetInput( self.xyGrid )
>    ... # render stuff
> 
> I get a flat structured grid on the display with no elevation.  It has colours 
> that make sense for the data, so I think it is correctly set up.
> 
> However, I can't figure out how to feed the xyGrid to vtkWarpScalar to warp it 
> using the scalar (or active scalar?).  It seems to have to go via a 
> vtkAlgorithm but when I try vtkDataObjectToDataSetFilter  then feed this to 
> vtkWarpScalar I get an empty data set.  The input xyGrid lists (on print) a 
> credible list of data and points, but the output from any of the filters I have 
> tried is nothing.
> 
> I'm wondering if something in my basic approach is off?  Should I be using a 
> vtkAlgorithm sub-class to create my structured grid, rather than creating it 
> directly?
> 
> Best regards
> -- Simon
> 


-- 
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Bryn Lloyd
Computer Vision Laboratory
ETH Zürich, Sternwartstrasse 7, ETF C110
CH - 8092 Zürich, Switzerland
Tel: +41 44 63 26668
Fax: +41 44 63 21199
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