[ITK-users] Smallest region containing the physical space covered by another image's region

[Cyril Mory]

Hi Matt,

Thank you for your detailed comments. I fixed most of the issues you 
spotted and amended the patch. Unfortunately, I was unable to move the 
method to itkImageRegion: from there I could not use the itkImageBase 
methods TransformIndexToPhysicalPoint and TransformPhysicalPointToIndex.

I am note familiar with forward declarations, friend classes and how 
they are meant to be used, so maybe it was possible indeed and I just 
did it wrong.

Cyril

On 04/15/2015 07:22 PM, Matt McCormick wrote:
> Hi Cyril,
>
> Thanks for contributing the patch!
>
> I added a comments for some minor things on Gerrit.  If it is more
> convenient to do the computations manually than use BoundingBox, that
> is fine. In terms of where to put it, the ImageRegion class may be a
> better spot than ImageBase since there already are the PadByRadius,
> ShrinkByRadius, and Crop methods. In terms of the name, perhaps
> EnlargeOverBox or similar may be better. This is not a Get method like
> other Get'ers, we avoid the passive 'ing verb, and Box or something
> similar indicates we have done the computation in physical space
> instead of index space, which "Region" may imply.
>
> Thanks,
> Matt
>
> On Wed, Apr 15, 2015 at 7:23 AM, Cyril Mory
> <cyril.mory at creatis.insa-lyon.fr> wrote:
>> Hi Matt,
>>
>> I have added such a method to itkImageBase, it is called
>> GetSmallestRegionContainingRegion. The patch is submitted on a branch with
>> the same name. I made my best, but I think it will require more improvements
>> than the previous one before it can get merged.
>>
>> In particular, I haven't used the itk::BoundingBox class, because from its
>> description it seems to handle only itk::Point. Should I convert indexes to
>> points, run the BoundingBox calculation, and convert back ?
>>
>> I'll wait for the comments
>> Cyril
>>
>>
>> On 04/13/2015 09:12 PM, Matt McCormick wrote:
>>> Hi Cyril,
>>>
>>>> I am preparing a patch for the itkWarpImageFilter, and I came to realize
>>>> that computing the requestedRegion of the inputs from the output's
>>>> requested
>>>> region is non trivial.
>>> Great job on the patch submission! :-)
>>>
>>>
>>>> - the displacement in the deformation field can be very large, in any
>>>> direction, ... therefore there is no choice but to load the full input
>>>> image
>>>> into memory (unless we want to go through the whole deformation field to
>>>> evaluate the maximum displacement, but in a method like
>>>> GenerateInputRequestedRegion we do not want such heavy processing)
>>>> => Input image's requested region should be the largest possible region
>>> Yes, this is a good assessment.
>>>
>>>
>>>> - the requested region in the deformation field, on the other hand, can
>>>> be
>>>> computed. But it is not trivial. If the output and the DF have identical
>>>> information (spacing, origin, direction), then the requested region in
>>>> the
>>>> DF should be copied from the output. If their information differs,
>>>> computing
>>>> the requested region would require a method to compute the smallest
>>>> rectangular region that contains the physical space covered by an other
>>>> image's region, the other image having (potentially) a different spacing,
>>>> origin and/or direction. Does such a method exist somewhere in ITK ?
>>> A possible approach here could transform all corner indexes of the
>>> output to physical space points, transform physical points to index
>>> space of the DF, and compute a bounding box of these index points.
>>>
>>> The methods to apply could be
>>>
>>>     TransformIndexToPhysicalPoint
>>>     TransformPhysicalPointToIndex
>>>
>>> on the ImageBase class and the itk::BoundingBox class.
>>>
>>>
>>> HTH,
>>> Matt
>>