How to determine the first vertex of a regular polygon drawn with vtk.vtkRegularPolygonSource()?

Or What is the projection direction of the coordinates of the first vertex of a regular polygon drawn with `vtk.vtkRegularPolygonSource()`

? Is it unique?e.g. [1,0,0] or [-1, 0, 0]?

@lassoan

Such low level details are probably not documented and subject to change, but you can see how this class works now by looking at its source code.