[Paraview] [vtk-developers] Temporal Redesign

[David Cole]

In the meantime, would you revert your change so we can otherwise approach
green on the VTK dashboard?
It seemed to be largely getting closer to green for about two weeks up till
that change and it would be nice to see the progress instead of having
TemporalFractal test failing everywhere it runs for the next several weeks.

Thanks,
David


2008/12/8 John Biddiscombe <biddisco at cscs.ch>

>  I made a few changes to TemporalShiftScale and SnapToTimeStep last week
> which had unfortunate repercussions for the TemporalFractal test.
>
> I've spent some time going over the executives and various classes which
> make use of TemporalData and I would like to make some changes to the whole
> temporal framework...
>
> Problems : The main problem with the temporal design as it stands is that
> it is very difficult to know when a filter has got the right input or output
> when temporal looping is involved. The problem is largely caused by the
> TemporalDataSetAlgorithm Family. These classes export a TemporalDataSet
> directly, and it isn't possible to know what kind of datatype they have
> inside the collection.
>
> Consider the case of the failing TemporalFractal Test.
> A TemporalFractal class exports TemporalDataSet. Currently, this can only
> be connected to another class which takes TemporalData as input. Even if it
> only exports a single timestep, which may be uniform grid, or rectilinear,
> or even a hierarchy of either (Multiblock etc)
>
> We would like the Executive to take temporal data and loop it for non
> temporal filters, but we can't connect a non temporal filter to it and get
> it right- because when the filters are connected together and first
> executed, the RequestDataObject pass for the filter accepting the
> TemporalDataSet doesn't know what type of output to create -  we fudged
> around this by simply exporting a temporal dataset too (which is why snap
> and shift scale were TemporalAlgorithms (and they should not be, they do not
> change the type of data passing through them). There are several bugs
> existing (http://public.kitware.com/mantis/view.php?id=6662) which all
> stem from the problem that the executive needs to take a single dataset from
> a temporal collection and pass it into a non temporal filter - currently it
> just doesn't do it and we see the output of a filter change to temporal
> within the paraview gui and various other side effects once temporal stuff
> is initiated.
>
> I'd am going to remove the whole TemporalDataSetAlgorithm family and
> instead have filters which declare themselves as (say)
> UniformGrid/Image/PolyData algorithms (or even multiblock), but export a new
> information key which says "I support temporal" if they are capable of
> delivering multiple time steps. Filters which require temporal collectios of
> type X, will add a key requesting time.
>
> The advantages of this are
> a) Filters will export a defined 'type', which other filters and the gui
> will be aware of, so temporal filters exporting polydata will be distinct
> from temporal filters exporting imagedata and so on. The user can then also
> write a filter which requires N Polydata and not any other type, currently
> the pipeline connects all temporal classes without checks.
> b) The checks in the executive will be simpler. A filter needs temporal
> data, but the upstream pipeline exports simple, so loop. When a filter needs
> simple, but upstream has declared time support, we take the i'th dataset on
> iteration i (or more correctly, the dataset with timestamp=t).
> c) Filters which support temporal activity (exporting more than one
> dataset) as in b) above can have their output dataobjects replaced by the
> executive and fill the N steps as before. We replace the code in the
> existing CheckDataObject() method which currently is incorrect (temporal
> IsA(composite) always returns true and causes untold trouble) and solve most
> of the outstanding temporal problems in one place (almost). Effectively we
> have, if filter supports temporal output and more than one steps were
> requested. change it - . If filter requires temporal and only one step
> exists, create temporal - the rest of the time, stop messing about. The
> current dataset swapping logic is a mess.
> d) existing filters(readers mainly) can be updated to support temporal
> natively with a pretty simple strategy. Add the temporal support flag, and
> in request data, generate N steps if required, and place them in the output.
> Much easier than the current option of creating a new class derived from
> TemporalDataSetAlgorithm and instantiating a reader inside it. (I'm talking
> here about generating multiple time steps from an existing reader - the
> executive can loop for you, but if you have a sophisticated file format,
> reading N at once can be desirable...)
>
> The changes the users will notice are
> vtkTemporalDataSetAlgorithm is removed, instead, filters which can *supply
> *multiple steps place an extra key TEMPORAL_OUTPUT_SUPPORTED in
> FillOutputInformation
> Filters which *require *multiple timesteps will place
> TEMPORAL_INPUT_REQUIRED during the FillInputInformation call. (Here' I think
> we might enhance the paraview GUI to allow a temporal input domain so that
> you can only instantiate temporal filters when connected to filters which
> are capable of supplying it). Filters such as temporal interpolator, become
> dataobject algorithms, likewise temporalcache.
>
> I believe this will solve a great many problems, though I have not
> considered the effect on TEMPORAL_FAST_PATH so please get back to me if this
> is going to be a problem.
>
> I will be working on this on the back burner until the new year no doubt,
> when I hope I have everything in order. The changes I have outlined above
> are of course subject to change as I encounter problems I've not considered.
> Please get in touch if you have strong feelings about this.
>
> JB
>
>
>
>
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