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

[Matt McCormick]

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
>
>
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