Ghosts and Extents (was [vtkusers] vtkImageImport in java?)

Steve M. Robbins steven.robbins at
Sun Jan 30 14:12:01 EST 2005


On Fri, Jan 28, 2005 at 03:25:44PM -0500, Steve M. Robbins wrote:

> Has anyone got example code that builds image data from scratch in Java?
> Ultimately I'd like a vtkImageData object.
> I considered using vtkImageImport in java but there doesn't appear to
> be any access to the two methods that actually copy data:
> CopyImportVoidPointer() and SetImportVoidPointer().  :-/

I went back to copying the data directly into a vtkImageData object
and finally managed to get things working.  It turns out that the only
bit that I had missed initially was to call SetWholeExtent().  Using
just SetExtent() is not enough, it seems.

I have read the VTK User's Guide.  The chapter on how the pipeline
operates is helpful, but I'm still not sure exactly what is the
distinction between "extent", "whole extent" and "update extent".  I
get the feeling that the update extent is set at the output end of the
pipeline (e.g. by mappers) and propagated backwards towards the source
objects, but even that is not clear.  Who is responsible for setting
the other two extents?  And what is a "ghost level"?

Is there any documentation that defines these terms?

How about source code: is there a particularly good class to start
with?  Data class?  Source class?  Reader?


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