[vtkusers] using different vtkPolyData point data for colouring and scaling glyphs

[Sherwood, P (Paul)]

Hi All,

I am trying to set up a vtkPolyData object (from 
a python script) and for each point set two scalar
arrays:
 - a float array to hold scale factors and
 - an int array to hold colours (used to index into a colour table)

I would like to visualise this array using a set of lines
connecting the points, which should be coloured using
the int array, and a set of sphere glyphs which are scaled
by the float array and coloured by the int array.

The problem I am having relates to setting up the both 
colour and scaling of the glyphs using different scalar
arrays.

Since I am associating two scalar arrays with each point I
assume I will need to give them names, which are 'col' and 'sizes'. 

I am not sure whether to associate them both to the
vtkPolyData Object's Point Data field using 
the AddArray method  (from vtkFieldData)  .. or
the SetScalar method (from VtkDaraSetAttributes)

Clearly I could use AddArray twice, or SetScalar once and AddArray
once (but not SetScalar twice).

At the moment I have code which uses AddArray twice. The lines
which are drawn by a mapper which takes its output from the
polydata object are OK using the following code:

m.SetScalarModeToUsePointfieldData()
m.ColorByArrayComponent('col',0)

But I don't know how to set the color and scale for the glyphs.
Applying the same commands to this mapper does not generate
any colour. An there doesn't seem to be a "ScaleByArrayComponent"
method anyhow.

Can anyone suggest the right approach please?

Incidentally (and perhaps this is relevant) I just found the following in
the
nightly docs:

doc>void vtkMapper::ColorByArrayComponent  (  const char *    arrayName,  
doc>  int    component 
doc> )   
doc> 
doc> Legacy: These methods used to be used to specify the array component. 
doc> It is better to do this in the lookup table

But so far I haven't found anything on how to set the array component
using the methods of the mapper.

When reading the documentation I wonder if there is a distinction any more
between "Point Data" and Point Field Data"?

I have attached my python script.

Thanks!

Paul Sherwood.


# to try this you may need to copy vtkRenderWidget.py from
# the Wrapping/Python directory into your PYTHONPATH.

from vtkpython import *
from Tkinter import *
from vtkTkRenderWidget import *

root = Tk()

# create vtkTkRenderWidget
root.pane = vtkTkRenderWidget(root)

# pack the pane into the tk root
root.pane.pack(side = 'top', expand=1, fill = 'both',padx=3, pady=3)

ren = vtkRenderer()
renwin = root.pane.GetRenderWindow()
renwin.AddRenderer(ren)

p = vtkPoints()
p.SetNumberOfPoints(5)
p.SetPoint(0,[0.,0.,0.])
p.SetPoint(1,[2.,0.,0.])
p.SetPoint(2,[0.,2.,0.])
p.SetPoint(3,[0.,0.,2.])
p.SetPoint(4,[2.,2.,2.])

l = vtkCellArray()
l.Allocate(6,6)

l.InsertNextCell(2)
l.InsertCellPoint(0)
l.InsertCellPoint(1)
           
l.InsertNextCell(2)
l.InsertCellPoint(0)
l.InsertCellPoint(2)

l.InsertNextCell(2)
l.InsertCellPoint(0)
l.InsertCellPoint(3)

l.InsertNextCell(2)
l.InsertCellPoint(1)
l.InsertCellPoint(4)

l.InsertNextCell(2)
l.InsertCellPoint(2)
l.InsertCellPoint(4)
           
l.InsertNextCell(2)
l.InsertCellPoint(3)
l.InsertCellPoint(4)

col = vtkIntArray()
col.SetNumberOfComponents(1)
col.InsertNextTuple1(0)
col.InsertNextTuple1(1)
col.InsertNextTuple1(2)
col.InsertNextTuple1(3)
col.InsertNextTuple1(4)
col.SetName('col')

sizes = vtkFloatArray()
sizes.SetNumberOfComponents(1)
sizes.InsertNextTuple1(1.)
sizes.InsertNextTuple1(1.2)
sizes.InsertNextTuple1(1.4)
sizes.InsertNextTuple1(1.6)
sizes.InsertNextTuple1(1.8)
sizes.SetName('sizes')

poly = vtkPolyData()
poly.SetPoints(p)
poly.SetLines(l)
poly.GetPointData().AddArray(col)
poly.GetPointData().AddArray(sizes)

# If I use this, I can scale the glyphs
# poly.GetPointData().SetScalars(sizes)

# If I use this, I can colour the glyphs but not
# scale them using the sizes field
poly.GetPointData().SetScalars(col)

print poly

# look table (red/green/blue/gray/yellow)
t = vtkLookupTable()
t.SetNumberOfColors(5)
t.Build()
t.SetTableValue(0,1,0,0,1)
t.SetTableValue(1,0,1,0,1)
t.SetTableValue(2,0,0,1,1)
t.SetTableValue(3,.5,0.5,0.5,1)
t.SetTableValue(4,1,1,0,1)

m = vtkPolyDataMapper()
m.SetInput(poly)
m.SetScalarRange(0.0, 4.0)
m.SetLookupTable(t)
# this seems to work
m.SetScalarModeToUsePointFieldData()
m.ColorByArrayComponent('col',0)

a = vtkActor()
a.SetMapper(m)
ren.AddActor(a)

#
# Add sphere glyphs
#
s = vtkSphereSource()
g = vtkGlyph3D()
g.SetInput(poly)
g.SetSource(s.GetOutput())

# This works but the colour array is used for scaling
# as well
g.SetColorModeToColorByScalar()

# need to find a way of choosing a particular array 
# there is no ScaleByArrayComponent 
#g.SetScaleModeToScaleByScalar()
#?? g.ScaleByArrayComponent('col',0)
g.SetScaleModeToDataScalingOff()

m = vtkPolyDataMapper()
m.SetInput(g.GetOutput())
m.SetScalarRange(0.0, 4.0)
m.SetLookupTable(t)

# try and colour it
# this seems not to work either
#m.SetScalarModeToUsePointFieldData()
#m.ColorByArrayComponent('col',0)

print 'Glyph', g
print 'Glyph mapper',m
act = vtkActor()
act.SetMapper(m)
act.PickableOff()
ren.AddActor(act)

root.mainloop()