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<p class="MsoNormal">Dear all,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The BSplineInterpolateImageFunction class has two functions to compute<br>
the derivative:<br>
- EvaluateDerivativeAtContinuousIndex<br>
- EvaluateValueAndDerivativeAtContinuousIndex<o:p></o:p></p>
<p class="MsoNormal">The first one does take direction cosines into account, the other does<br>
not. When called while using an image with non-trivial direction<br>
cosines, the two derivatives are not equal.<o:p></o:p></p>
<p class="MsoNormal">I believe this bug was introduced a long time ago by commit 6abbc7969a90786c4c73f5d191f634db536c2d1d :<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><a href="http://itk.org/gitweb?p=ITK.git;a=commitdiff;h=6abbc7969a90786c4c73f5d191f634db536c2d1d#patch13">http://itk.org/gitweb?p=ITK.git;a=commitdiff;h=6abbc7969a90786c4c73f5d191f634db536c2d1d#patch13</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I attached a test program that simply calls the two functions. The input of the test program (set with interpolator->SetInputImage() ) is an image with direction cosines:<o:p></o:p></p>
<p class="MsoNormal">(-0, 7.48376e-009, -1, 7.48376e-009, 1, 7.48376e-009, 1, -7.48376e-009, 0)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Current output:<o:p></o:p></p>
<p class="MsoNormal">EvaluateDerivative: [42.7697, -9.97885, 22.2913]<o:p></o:p></p>
<p class="MsoNormal">EvaluateValueAndDerivative: [-22.2913, -9.97885, 42.7697]<o:p></o:p></p>
<p class="MsoNormal">But that should really be the same. Note that the first and third entry are switched, and negated.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I filed a gerrit entry which proposes a fix:<o:p></o:p></p>
<p class="MsoNormal"><a href="http://review.source.kitware.com/#/c/11016/">http://review.source.kitware.com/#/c/11016/</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">After that fix the output is as follows:<o:p></o:p></p>
<p class="MsoNormal">EvaluateDerivative: [42.7697, -9.97885, 22.2913]<o:p></o:p></p>
<p class="MsoNormal">EvaluateValueAndDerivative: [42.7697, -9.97885, 22.2913]<o:p></o:p></p>
<p class="MsoNormal">So, equal as it should be.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Looking forward to your feedback,<o:p></o:p></p>
<p class="MsoNormal">Regards, Marius<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-GB">Marius Staring, PhD<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Division of Image Processing (LKEB)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Department of Radiology<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Leiden University Medical Center<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">PO Box 9600, 2300 RC Leiden, The Netherlands<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">phone: +31 (0)71 526 2137, fax: +31 (0)71 524 8256<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">m.staring@lumc.nl<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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