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

[Simon Clift]

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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