[Insight-developers] Meta data dictionary passing through the ITK pipeline

[Miller, James V (GE, Research)]

Hans, 

Doug Alan and Mike Halle are using the meta data dictionary mechanism to
pass coordinate frame mappings for astronomical data into ITK.  These
coordinate frames are nonlinear.   They are hitting on an issue that the
meta data dictionary is not passed through the ITK pipeline.

Historically, this data has not been passed through for several reasons:

*	A given filter may not understand the context of the meta data.
Therefore, the filter is not in a position to know whether the meta data
is still valid after the filter.  For instance, lets say one of the
fields in the meta data encodes pixel size.  A resampling or scaling
filter may not know to look for a particular tag to change its value
when moving the dictionary from input to output.  Other more subtle
examples are conceivable where filters ignore particular meta data
fields and the fields get passed from input to output but are no longer
valid for the data being processed.
*	Copying the meta data dictionary may be expensive.  It could be
a lot of data.

I can see a few options here.

1. Blindly copy the meta data dictionary from input to output and buyer
beware.

2. Put in a mode to the pipeline to turn on copying the meta data
dictionary.  This would be off by default but could be turned on when
people want the meta data dictionary to move through the pipeline.

3. Devise a naming convention or other attribute mechanism to label
fields in the dictionary to indicate which fields can be copied by a
filter.  This could be a global approach where fields with a standard
prefix are copied or could be more generic where people could say to
copy fields with this prefix or that prefix at runtime.

4. Expand the list of image parameters (spacing, origin, orientation)
stored in an itk::Image to include something that will work for what
Doug and Mike need.

I'd like to discuss this on the ITK tcon this week.  Are you available?

Jim

Jim Miller 
_____________________________________
Visualization & Computer Vision
GE Research
Bldg. KW, Room C223
1 Research Circle, Niskayuna NY 12309-1027

millerjv at research.ge.com <mailto:millerjv at research.ge.com>
(518) 387-4005, Dial Comm: 8*833-4005
Cell: (518) 505-7065, Fax: (518) 387-6981


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