[vtkusers] How to get vtk file from scattered points?

[ya ya]

I just begin to learn vtk. Now something about the file format beats me.
Recently I've learned the format of the vtk files, for example, 
vtkImageData, vtkPolyData, vtkUnstructuredGrid etc. in the vtk Userguide. 
But I wonder how I can gain such kinds of format? If I want to create a 
terrian and I've got many scattered points in the form of coordinate, what 
should I do next? Do I have to change the format into vtk file format? If 
so, how can I change the format?  
Please give me some help, thank you!


                                                                            
       Ivy

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