No subject

compares the true transform parameters not to exceed thresholds --
0.025 for scale and 1.0 for translations.


On Wed, Jan 28, 2009 at 11:30 AM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
> Also, their can be multiple baselines for a given test. If you look at:
>
> http://public.kitware.com/cgi-bin/viewcvs.cgi/Testing/Data/Baseline/Registration/?root=Insight
>
> you will see that some tests have multiple baselines because of the
> type of variability discussed in this thread.
>
> For example, ImageRegistration13Test has 5 baselines.
>
> Bill
>
> On Wed, Jan 28, 2009 at 11:14 AM, Blezek, Daniel J.
> <Blezek.Daniel at mayo.edu> wrote:
>> Just 2 cents here.
>>
>> 1) For a linear registration, you could expect the registration results
>> to be ~0.1 degrees and ~0.1 mm cross platform.  The major source of this
>> problem is differences in floating point representations under different
>> compilers/hardware.  I shouldn't worry about this, it'd be difficult for
>> a human to see.  For something like BSplines, you might have a bit more
>> error.
>>
>> 2) A very simple way to do this is to do a forward transformation using
>> one transform (ground truth), then the inverse transform of the newly
>> calculated transform.  I think this is called Target Registration Error
>> by Fitzpatrick and Co., but you should look it up.  This is where you
>> need to decide on your tolerance.  As Karthik mentioned, only simple ITK
>> transforms have an inverse, which is really a shame.  They are so
>> useful, even if they are numeric.
>>
>> 2a) I suppose you could forward transform the same point using two
>> different transforms and see how far apart they are.  This seems
>> reasonable, but you'd have to sample a bunch of points to account for
>> rotation, and transform centers, etc.  And you'd only get a distance
>> measure, not a rotational measure.
>>
>> For transforms with an inverse, you can do what you are asking, and it
>> would be a valuable contribution to ITK, but it's not general, as not
>> all transforms support an inverse.  And you could always test the
>> transform you care about...
>>
>> Incoherent as usual,
>> -dan
>>
>> -----Original Message-----
>> From: insight-users-bounces at itk.org
>> [mailto:insight-users-bounces at itk.org] On Behalf Of Andriy Fedorov
>> Sent: Tuesday, January 27, 2009 6:18 PM
>> To: ITK Users
>> Cc: Miller, James V (GE, Research)
>> Subject: [Insight-users] Rigid registration testing and reproducibility
>>
>> Hi,
>>
>> I would like to do regression tests of rigid registration with real
>> images, and compare the result with the baseline transform. Here are two
>> related questions.
>>
>> 1) ITK registration experts, could you speculate on what is the normal
>> variability in the rigid registration results run with the same
>> parameters, metric initialized with the same seed, when run across
>> different platforms? What could be the sources of this variability,
>> given the same initialization and same parameters?
>>
>> 2) If I understand correctly, the current testing of registration that
>> comes with ITK generates a synthetic image with known transform
>> parameters, which are compared with the registration-derived transforms.
>>
>> The testing framework implemented in itkTestMain.h allows to compare
>> pixelwise two images, but this does not seem to be practical for
>> registration regression testing, because of the variability in the
>> registration results I mentioned earlier. Accounting for this
>> variability using tolerance values of just 1 pixel hugely increases the
>> test runtime, but in my experience, the comparison may still fail.
>>
>> Would it not make sense to augment itkTestMain.h with the capability to
>> compare not only images, but transforms? Is this a valid feature
>> request, or am I missing something?
>>
>> Thanks
>>
>> Andriy Fedorov
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>