[Insight-users] UnaryFunctorImageFilter and MetaDataDictionnary

[Julien Michel]

Bill Lorensen a écrit :
> Luis,
> 
> I think this change should be removed. Julien wants the
> MetaDataDictionary copied through the pipeline. CopyInformation just
> copies the "meta" information (spacing, origin, direction, regions,
> etc.).
> 
> We never provided the facility to pass the MetaDataDictionary through
> the pipeline. I think we determined that the MetaDataDictionary could
> get out of sync with the processed data as it passed through the
> pipeline.
> 
> The current change is causing CastImageFilter to fail if the
> dimensions of the input and output do not match.

Ok, instead of submitting possible fix, let me state our problem.

We are developping an ITK based library to process remote sensing images
(mainly from satellites).

These data comes with a lot of geo-information such as sensor position
and date, group control points or map projection parameters.

We needed to store these information so as to be able to reproject the
data in other geometry (one of the most useful feature is called
orthorectification and reproject image from raw geometry to an image
superimposable to a map).

In our Image class deriving from itk::Image, we choosed to store these
information in the MetaDataDictionnary for convenience but this is
really not the main part of the problem.

Now, UnaryFunctorImageFilter does only pixel-wise transformation, so all
the geoinformation remains valid even at the end of a pipeline
containing several filters deriving from UnaryFunctorImageFilter. But
with the current implementation of this filter, there is no possible way
to get these data passed through the pipeline.

Of course, we could set these information by hand each time we use a
UnaryFunctorImageFilter, but that makes really a lot of code
(UnaryFunctorImageFilter subclasses are rather common, in ITK or in our
own library).

We could also rewrite every ITK subclasses of UnaryFunctorImageFilter
(and constrain input and output dimension) but I think this is really
not the point of using a powerful library like ITK.

So we are looking for a way to make UnaryFunctorImageFilter pass trough
some meta-information known to be still valid after pixel-wise operations.

This might as well apply to other kind of data. Maybe medical imaging
comes with information such as acquisition date, or physiological
parameters from the patient that could be used later on by some filters.

I understand that my solution is not perfect, and I would be glad to
read any other suggestions (appart from the "by hand" thing).

Thank you very much,

Julien
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Julien MICHEL - Ingénieur d'études - Traitement d'images
CS Systèmes d'Information - Division ESPACE
Département Information Géographique & Image
Téléphone : +33 561 17 64 27
Email : julien.michel at c-s.fr

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