[vtk-developers] GetOutput().GetWholeExtent()

[David Gobbi]

Hi Berk,

I think that a good general rule is that there should be a convenience
function for each key that is likely to be accessed from application
code.  Application code can use the convenience functions, while VTK
filters/mappers should aim to consistently use the keys to get the
information directly.

Because GetWholeExtent() pops up all the time in application code, it
should exist as convenience method, but it's tough to say where it
should go.  In image-display apps, people use streaming all the time,
but they always want to know how big the full data set it.

I would go so far as to suggest that WHOLE_EXTENT be part of the data
object information.  It is an important piece of information to have
when dealing with a data object, unlike UPDATE_EXTENT which is only
important to the executive.

 - David



On Wed, Apr 4, 2012 at 6:34 PM, Berk Geveci <berk.geveci at kitware.com> wrote:
> Thank you David.
>
> I have been working on a set of documents to help migration to VTK 6. One
> thing that I noticed while working on these is that the way we access this
> sort of meta-data is fairly inconsistent. There are some convenience
> functions in vtkDataObject, vtkStreamingDemandDrivenPipeline etc. to set/get
> meta-data and some of them are accessed directly. I am too burned out to
> tackle this right now but it is something to think about...
>
> -berk
>
>
> On Wed, Mar 28, 2012 at 7:25 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>
>> Adding a hint for Get(vtkInformationIntegerVectorKey *) turned out to
>> be straightforward.. I have a patch in gerrit that allows Get to be used
>> with all IntegerVector and DoubleVector keys so that WHOLE_EXTENT,
>> SPACING, ORIGIN, etc. can be used from the wrappers.  I'll probably
>> merge tomorrow.
>>
>> A more general solution, i.e. one that also encompasses IntegerPointer
>> keys (yikes!) will have to wait...
>>
>>  - david
>>
>>
>>
>> On Wed, Mar 28, 2012 at 3:46 PM, David Gobbi <david.gobbi at gmail.com>
>> wrote:
>> > You mean a generic "pointer" object that can be used from Python.
>> >
>> > In Python 3, there is a special object called "memoryview" that can be
>> > used for this purpose, so that's the direction that I've considered
>> > going.  I'd like to avoid generic pointer wrapping, because it makes
>> > it too easy to crash the program from python.  I know that SWIG wraps
>> > pointers, but I've made a conscious choice not to do the same for the
>> > VTK wrappers.
>> >
>> >  - David
>> >
>> >
>> > On Wed, Mar 28, 2012 at 3:32 PM, Pat Marion <pat.marion at kitware.com>
>> > wrote:
>> >> Hi David,
>> >>
>> >> What about making a generic way to access these kinds of arrays, given
>> >> a
>> >> length argument, using ctypes or numpy?
>> >>
>> >> Something like:
>> >>
>> >> length = info.Length(key)
>> >> myarray = vtk.array_from_pointer(info.Get(key), length)
>> >>
>> >>
>> >> Pat
>> >>
>> >>
>> >> On Wed, Mar 28, 2012 at 4:08 PM, David Gobbi <david.gobbi at gmail.com>
>> >> wrote:
>> >>>
>> >>> Hmm, I just noticed something in my own code.  The following method
>> >>> isn't wrapped, because it returns a bare pointer.  As a result the
>> >>> WHOLE_EXTENT key can't be used with Get:
>> >>>
>> >>> int * vtkInformation::Get(vtkInformationIntegerVectorKey *);
>> >>>
>> >>> But I think that I can add a wrapper hint to get it working... the
>> >>> wrappers can internally query the Length() method to figure out what
>> >>> number of values to return.
>> >>>
>> >>>  - David
>> >>>
>> >>>
>> >>> On Fri, Mar 23, 2012 at 10:44 AM, Philippe Pebay
>> >>> <philippe.pebay at kitware.com> wrote:
>> >>> > Thanks Bill.
>> >>> >
>> >>> > Philippe
>> >>> >
>> >>> >
>> >>> > On Fri, Mar 23, 2012 at 4:49 PM, Bill Lorensen
>> >>> > <bill.lorensen at gmail.com>
>> >>> > wrote:
>> >>> >>
>> >>> >> This page has a suggested replacement.
>> >>> >> http://vtk.org/Wiki/VTK/VTK6/Migration/WikiExamples#Improve
>> >>> >>
>> >>> >> On Fri, Mar 23, 2012 at 8:23 AM, Philippe Pebay
>> >>> >> <philippe.pebay at kitware.com> wrote:
>> >>> >> > Hello all
>> >>> >> >
>> >>> >> > GetOutput().GetWholeExtent() does not work any longer in VTK 6. I
>> >>> >> > have q
>> >>> >> > boatload of vtkpython scripts using this! Does anyone know what
>> >>> >> > the
>> >>> >> > quick
>> >>> >> > fix is?
>> >>> >> >
>> >>> >> > Thanks
>> >>> >> > Philippe
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