[vtkusers] Picking points from multiple surfaces.

[安 继业]

Hi.

I have extracted multiple isosurfaces from a data set by vtkContourFilter, 
just as the vtk examples Medical/Medical2.cxx illustrated. Now I want to 
pick points from the displayed surfaces. I use a vtkPropCollectionto manage 
all the vtkActor objects, each of them represents a single isosurface.

1. I am not so familiar with vtk till now. Can anyone tell me which kind of 
pickers should I use? There are a hierarchy of picking classes in vtk, like 
vtkCellPicker, vtkPointPicker, and so on. In my application, I just want to 
retrieve coordinates from each surface in the rendering window. Of course 
when the coordinates returned, I must know which surface this point belongs 
to.

2. If I extract 2 surfaces from one data set, and 2 surfaces from another 
dataset, can I display them together? Simply by add the 4 separate actors 
to the rendering window? And are the 4 isosurfaces of the same coordinate 
system? For example, if I pick a point from one surface from the surface of 
the first data set and get it's coordinate (1, 1, 1), and another point 
from the surface of the second dataset with coordinate (2, 2, 2), so can 
these two coordinates be compared to calculate the shift between the two 
data sets?

Any suggestion will be appreciated. Thank you in advance.

Jiye An

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