[vtkusers] Re: Re: newbie question : vtkPlanes to represent a cube

[Goodwin Lawlor]

Hi Jim,

> ERROR: In /home/jim/VTK/VTK/Filtering/vtkImplicitDataSet.cxx, line 78
> vtkImplicitDataSet (0x829ae88): Can't evaluate dataset!

This filter needs the input to have a set a scalars, presumably representing
a distance function.


> But if I don't try to display the actor, I
> don't get any error (which may be normal since I don't yet fully
> understand how VTK works).

That's because the pipeline hasn't been asked to execute by the renderer.

I had another look at the first method you tried using vtkPlanes... There is
some unusual behavior here that I dont have time to go through but you can
play with this code... contour values of -0.75 work but values >-0.75 crash
the contour filter. Looking at the input data to the contour as an image is
looks like vtkPlanes has trouble evaluating the function where it is
equidistant from 3 planes. I am not sure you had the point values correct
either:

package require vtk

vtkPoints points
    points SetNumberOfPoints 6
    points SetPoint 0 1 0 0
    points SetPoint 1 -1 0 0
    points SetPoint 2 0 1 0
    points SetPoint 3 0 -1 0
    points SetPoint 4 0 0 1
    points SetPoint 5 0 0 -1
vtkFloatArray norms
    norms SetNumberOfComponents 3
    norms SetNumberOfTuples 6
    norms SetTuple3 0 1 0 0
    norms SetTuple3 1 -1 0 0
    norms SetTuple3 2 0 1 0
    norms SetTuple3 3 0 -1 0
    norms SetTuple3 4 0 0 1
    norms SetTuple3 5 0 0 -1

vtkPlanes planes
    planes SetPoints points
    planes SetNormals norms

vtkSampleFunction sample
    sample SetImplicitFunction planes
    sample SetModelBounds 2 -2 2 -2 2 -2
    sample SetSampleDimensions 40 40 40
    sample Update

vtkImageViewer viewer
    viewer SetInput [sample GetOutput]
    viewer SetColorWindow 2
    viewer SetColorLevel 0
    viewer SetZSlice 2
    viewer Render

scale .s -command cb
pack .s

proc cb {var} {
    viewer SetZSlice $var
    viewer Render
}

vtkContourFilter contour
    contour SetInput [sample GetOutput]
    contour SetValue 0 -0.75
vtkPolyDataMapper mapper
    mapper SetInput [contour GetOutput]
vtkActor actor
    actor SetMapper mapper
    [actor GetProperty] SetRepresentationToWireframe
vtkRenderer ren
    ren AddActor actor
vtkRenderWindow renwin
    renwin AddRenderer ren
vtkRenderWindowInteractor iren
    iren SetRenderWindow renwin
    iren AddObserver UserEvent {console show}
    iren Initialize