[vtkusers] Re: problem viewing merged PolyData sets using

[Goodwin Lawlor]

Hi Denis,

I looked up the source to vtkGlyph3D and vtkAppendPolyData...

You're right- vtkGlyph3D can use a vtkPolyData with just points set and no
topology.

The problem you seeing is because vtkAppendPolyData appends cells to its
output and so needs topology...

here's the code from vtkAppendPolyData

  if ( numPts < 1 || numCells < 1 )
    {
    //vtkErrorMacro(<<"No data to append!");
    return 1;
    }

maybe that error macro should be changed to a debug macro and uncommented?

Sorry for the confusion,

Goodwin

"Denis Saussus" <saussus at skynet.be> wrote in message
news:b004f848d9c67ed63cdbd70ee72f6b37 at skynet.be...
Thanks for the replies Goodwin. You say that vtkGlyph3D needs both geometry
and topology to work -- is that really true? How come the code fragment I
posted works just fine as long as the input to vtkGlyph3D is the original
vtkPolyData object (made manually with just points) and NOT the output of
vtkAppendPolyData().GetOutput() ?

Anyway, here is the how I created the vtkPolyData objects.

import RandomArray

points = vtk.vtkPoints()
for n in range(1000):
x,y,z = [ RandomArray.normal(0, 1) for i in range(3) ]
points.InsertPoint(n, x, y, z)
a = vtk.vtkPolyData()
a.SetPoints(points)

... and so on for b = vtk.vtkPolyData()

Let me clarify the problem what is at the heart of the problem (I think ;)

This works:
...
a = vtk.vtkPolyData()
a.GetNumberOfPoints()
...

This does not work: Why?
...
a = vtk.vtkPolyData()
apd = vtk.vtkAppendPolyData()
apd.AddInput(a)
apd.GetOutput().GetNumberOfPoints()



Can you post the code where you've added points to the vtkPolyData objects?


"Denis Saussus" <dsaussus at fugro-jason.com> wrote in message
news:F42290EAAE100A4A99A3A9BE2059504FBDB121 at MAIL.fugro-jason.local...
How can I get the following to print the total
number of points in the appended set?

a = vtk.vtkPolyData()
b = vtk.vtkPolyData()

apd = vtk.vtkAppendPolyData()
apd.AddInput(a)
apd.AddInput(b)

print apd.GetOutput().GetNumberOfPoints()

==> this prints '0' instead of a+b ?

I tried doing apd.Update() before but it didn't help.

What am I missing?


i Denis,

At a guess, I would say your vtkPolyData's have points (geometry) but no
vertices (topology). vtkGlyph3D needs both to work, although in theory it
should only need the points.

Here's a trick to get it to work:

...
...
apd = vtk.vtkAppendPolyData()
apd.AddInput(somePolyData)
apd.AddInput(someMorePolyData)

verts = vtk.vtkMaskPoints()
verts.SetInput(apd.GetOutput())
verts.GenerateVerticesOn()
verts.SetOnRatio(1)

aSphere = vtk.vtkSphereSource()
aSphere.SetRadius(1.0)

spheres = vtk.vtkGlyph3D()
spheres.SetInput(verts.GetOutput())
spheres.SetSource(aSphere.GetOutput())

...
...


hth

Goodwin
"Denis Saussus" <dsaussus at fugro-jason.com> wrote in message
news:F42290EAAE100A4A99A3A9BE2059504FBDB11C at MAIL.fugro-jason.local...
I am plotting a vtkPolyData set containing 3d points so that
they display as spheres. I can get this to work very easily.

Now I have two vtkPolyData sets, each containing 3d points.
I want to plot them using a single mapper/actor. I am doing this
simply by using vtkAppendPolyData to merge the two sets into
one. My problem is that now nothing shows up.

Below is the script I am using. Help greatly aprpeciated...




##########################
# Why does this not work?
##########################

somePolyData = vtk.vtkPolyData()
# assume this contains some valid 3d points

apd = vtk.vtkAppendPolyData()
apd.AddInput(somePolyData)
apd.AddInput(someMorePolyData)

aSphere = vtk.vtkSphereSource()
aSphere.SetRadius(1.0)

spheres = vtk.vtkGlyph3D()
spheres.SetInput(apd.GetOutput())
spheres.SetSource(aSphere.GetOutput())

mapSpheres = vtk.vtkPolyDataMapper()
mapSpheres.SetInput(spheres.GetOutput())

spheresActor = vtk.vtkActor()
spheresActor.SetMapper(mapSpheres)

ren = vtk.vtkRenderer()
ren.AddActor(spheresActor)
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)
iren.Initialize()
renWin.Render()
iren.Start()



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