[vtkusers] How to use the docs efficiently as a newbie to vtk?

[lynx.abraxas at freenet.de]

Hello vtk programmers!


I  just  tried to figure out how I could have managed to get normals of a mesh
without any examples. Since then I feel very lost...
Concider one is a newbie to vtk and somehow one got  an  instance  of  a  mesh
(vtkPolyData).
Now I want to get a list of all the cell normals so I'd do as follows:

- Search in the class index (http://www.vtk.org/doc/nightly/html/classes.html)
for anything containing normal; I'd find vtkPolyDataNormals
- There I get to know it does what I need (if I select correct switches)
- I've learned that the result is in .GetOutput() which isn't mentioned  there
so I look in the superclass (vtkPolyDataAlgorithm)
-  In  vtkPolyDataAlgorithm  I  find  GetOutput()  which  yiels an instance of
vtkPolyData

--There I have the first disappointment: The output is not the normals...

- So I go to vtkPolyData: There I  don't  find  anything  having  to  do  with
normals so I go to the super class again (vtkPointSet)...
- In vtkPointSet nothing so up to vtkDataSet
- In vtkDataSet I find GetCellData()

--It  needs  some  abstract thinking to see that its result leads closer to my
normals...

- Having some vtkCellData I go on to vtkCellData Class Reference
- Nothing about normals there so I go up to vtkDataSetAttributes
- Finally I find GetNormals(); it returns vtkDataArray

--Now I wonder: What is vtkDataArray???

- I go vtkDataArray Class Reference: Seems to hold any kind of data array...

--How then do I know what data type is in the array that GetNormals() returns?
Is  it  char, int, float, double...? In the exampe vtkFloatArray::SafeDownCast
is used. Why not vtkDoubleArray::SafeDownCast? How would I know it's not  some
integer?  (I  know  for normals that wouldn't make much sense but else where I
might not be able to exclude this so easily)


Well, now, after showing my way through the labyrinth, my big question:
Is this the way You all go if You can't find an example for Your problem?
Can all this  be done much easier?
Since I know a bit of blenders API I  must  say  there  the  way  through  the
labyrinth is much more straight forward.

Just  getting  to  my  own  simple  vtk-program  by plugging parts of examples
together makes me feel very clumsy and lost. How to improve in this?


Thaks for any help and advice on this.
Lynx