[Insight-developers] instantiating itkVector

[Luis Ibanez]

Hi Richard,

The variable size vector and matrix that are available at this point
are the "vnl_vector" and "vnl_matrix".

The ITK variable length vector was not conceived as a class for
performing linear algebra operations.


   Regards,


      Luis


----------------------
Richard Beare wrote:
> It is difficult to be certain about performance issues at this stage,
> but I can make some guesses. The critical issue is having matrix maths
> available.
> 
> I'm actually coding up the SIFT algorithms - there was an IJ
> publication about this a while back, but it doesn't appear
> particularly good.
> 
> The matrix maths part is applied on a per feature basis, rather than a
> per voxel basis, so I don't expect it to be a big part of the
> execution time.
> 
> Is there a variable length itk vector that can be used in conjunction
> with a variable size matrix while allowing matrix algebra?
> 
> On Sun, Dec 7, 2008 at 9:55 AM, Luis Ibanez <luis.ibanez at kitware.com> wrote:
> 
>>Richard,
>>
>>You may have to consider how visible this class is supposed to be
>>and what performance implications you can anticipate from its
>>construction (e.g. is the type of class that you will use to
>>create thousands of instances in an inner loop ?).
>>
>>Using one of vcl vector classes that you can resize at run-time
>>is definitely an option. It is worth to write a small use case
>>example to see which one will work better.
>>
>>Note as well that ITK has the variable length vector, whose
>>size can be defined at run time.
>>
>>
>>  Regards,
>>
>>
>>      Luis
>>
>>--------------------
>>Richard Beare wrote:
>>
>>>Am I likely to be better off using underlying vcl classes directly?
>>>Will that give me more flexibility?
>>>
>>>On Sat, Dec 6, 2008 at 4:26 AM, Luis Ibanez <luis.ibanez at kitware.com>
>>>wrote:
>>>
>>>
>>>>Hi Richard,
>>>>
>>>>Thanks for the clarification.
>>>>
>>>>
>>>>This is good news and bad news  :-)
>>>>
>>>>
>>>>
>>>>The good news is that you know the number at compile time,
>>>>since that is what the itkVector instantiation will require.
>>>>
>>>>The bad news is that the expression that you need to evaluate
>>>>for computing the vector size is a non-trivial one.
>>>>
>>>>
>>>>One potential way of generating that computation would be to
>>>>have a Traits helper class, at the image of the NumericTraits
>>>>class.
>>>>
>>>>In this helper class you could define explicit instantiations
>>>>such that an internal enum (or static int) will be initialized
>>>>to the value of 3^(N-1).
>>>>
>>>>This is a bit manual, but I'm assuming that you would not need
>>>>more that dimensions in the range N=1,2,3,4,5 ... (?).
>>>>So you will be done with the Traits in a couple of copy/pasting
>>>>sessions, and in less than 50 lines of code.
>>>>
>>>>There are probably smarter ways of getting this to work,
>>>>but more coffee may be required for figuring them out...
>>>>
>>>>
>>>>  Regards,
>>>>
>>>>
>>>>      Luis
>>>>
>>>>
>>>>
>>>>----------------------
>>>>Richard Beare wrote:
>>>>
>>>>
>>>>>Hi,
>>>>>
>>>>>In this case I'll know it at compile time - it is dependent on the
>>>>>dimensionality of the image. Actually, to be specific, it is given by
>>>>>3^(ImType::ImageDimension - 1).
>>>>>
>>>>>It would probably look neater in the code if I could do it in a way
>>>>>that was not dependent on compile time knowledge, but I'm not sure
>>>>>that is possible. I'll need to do something equivalent with matrix
>>>>>types too.
>>>>>
>>>>>On Fri, Dec 5, 2008 at 12:50 AM, Luis Ibanez <luis.ibanez at kitware.com>
>>>>>wrote:
>>>>>
>>>>>
>>>>>
>>>>>>Richard,
>>>>>>
>>>>>>
>>>>>>Would you know the size of the neighborhood at compilation time ?
>>>>>>
>>>>>>or only at run-time ?
>>>>>>
>>>>>>
>>>>>>Please let us know,
>>>>>>
>>>>>>
>>>>>>Thanks
>>>>>>
>>>>>>
>>>>>> Luis
>>>>>>
>>>>>>
>>>>>>----------------------
>>>>>>Richard Beare wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>>Hi,
>>>>>>>I need to create a vector type with length equal to the size of a
>>>>>>>neighborhood - i.e. 3^ImageDimension. I suspect that there needs to be
>>>>>>>some sort of trick with macros, because calling pow is no good. Any
>>>>>>>suggestions?
>>>>>>>
>>>>>>>Thanks
>>>>>>>_______________________________________________
>>>>>>>Insight-developers mailing list
>>>>>>>Insight-developers at itk.org
>>>>>>>http://www.itk.org/mailman/listinfo/insight-developers
>>>>>>>
>>>>>>
>