[vtk-developers] Question about DATA_RESOLUTION key

[David E DeMarle]

Hello,

My suggestion is to ask for the update extent in the scaled down space
which is [0,127,0,127,0,0] in your example.
But be warned, I haven't used it with structured extents directly and
I'm not sure how it will behave. In my work I've always been working
inside ParaView where the requests start out as unstructured piece
requests but then make it back and are translated along the way before
they get to the structured readers that I've been working with so far.


Here are more details:

In the ParaView source code, see
vtkStreamingHarness::ComputePiecePriority() for an example of how I
drive the pipeline to ask for a particular piece at a particular
resolution.

That first tells the pipeline it is interested in a particular piece
at a particular resolution via the UPDATE_PIECE,
UPDATE_NUMBER_OF_PIECES, and UPDATE_RESOLUTION keys.

It then calls vtkStreamingDemandDrivenPipeline::ComputePriority()
where I've put the various pipeline passes that make the pipeline flow
just the way I needed it to.

ComputePriority eventually makes the reader's RequestInformation().
There the reader figures out what the real whole extent is as it
normally would, but then it uses a more or less arbitrary function to
decide what it should pretend the whole extent is based on the real
whole extent and the UPDATE_RESOLUTION key. Afterward it provides that
scaled down whole extent to the pipeline and from there on all
requests take place in the scaled down space.

Eventually RequestUpdateExtent and RequestData get called, and both
are within the scaled down space.

David E DeMarle
Kitware, Inc.
R&D Engineer
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x109



On Mon, Jul 25, 2011 at 2:54 PM, David Gobbi <david.gobbi at gmail.com> wrote:
> Hi Dave,
>
> I have a question about the way that UPDATE_RESOLUTION and
> UPDATE_EXTENT are used with 3D extents.  My intent is to have certain
> image filters and mappers request a desired UPDATE_RESOLUTION.
> But I'm not sure exactly how this ties in with UPDATE_EXTENT.
>
> For example: let's say that the full-resolution 3D extent is [0, 255,
> 0, 255, 0, 0] and a mapper wants half-resolution.  Should it request
> an UPDATE_RESOLUTION of 0.5 but keep the UPDATE_EXTENT
> at [0, 255, 0, 255, 0, 0]?  And would the updated data then have an
> extent of [0, 127, 0, 127, 0, 0]?
>
>  - David
>