PERF: less strict heuristic for valid points check

[stnava]

The previous check was overly strict. For example, one may be using a small mask (e.g. hippocampus) to focus registration within a much larger image. The registration result can be valid in this case despite a relatively small number of points used. Another alternative to this request would be to remove this check entirely.

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• COMP: compiler error or warning fix
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• PERF: performance improvement
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• WIP: Work In Progress not ready for merge

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[blowekamp]

I believe the ideal solution may be to have a "minimum overlap" parameter, in all the metrics.

It is quite a common error for the initial registration to have no overlay. It is also not uncommon for an optimization to go awry resulting in little to no overlap.

[thewtex]

Thanks for contributing this improvement @stnava 👍

We are still polishing the GitHub CI and have not finished the transition to GitHub quite yet -- the testing may give false positives until then.

[stnava]

practically speaking, i think we are erring on the wrong side here - rejecting too many valid registration setups as invalid. we've had several complaints about this and users have ultimately gone on to modify their own ITK copy.

[thewtex]

Pushed to Gerrit here:

http://review.source.kitware.com/#/c/23580/

[thewtex]

This has been merged.