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<div>Marius,</div>
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<div>GREAT CATCH. I'm working on incorporating your test into ITK right now in order to demonstrate both the bug and the solution.</div>
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<div>Hans</div>
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<div style="font-family:Consolas,monospace; font-size:12px">Hans J. Johnson, Ph.D.</div>
<div style="font-family:Consolas,monospace; font-size:12px">Assistant Professor, Department of Psychiatry</div>
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<div style="font-family:Consolas,monospace; font-size:12px">W274 GH Email: <a href="mailto:hans-johnson@uiowa.edu">hans-johnson@uiowa.edu</a></div>
<div style="font-family:Consolas,monospace; font-size:12px">200 Hawkins Drive Phone: (319) 353 8587</div>
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<span style="font-weight:bold">From: </span>"<a href="mailto:M.Staring@lumc.nl">M.Staring@lumc.nl</a>" <<a href="mailto:M.Staring@lumc.nl">M.Staring@lumc.nl</a>><br>
<span style="font-weight:bold">Date: </span>Wednesday, April 24, 2013 8:33 AM<br>
<span style="font-weight:bold">To: </span>ITK <<a href="mailto:insight-developers@itk.org">insight-developers@itk.org</a>><br>
<span style="font-weight:bold">Subject: </span>[Insight-developers] Bug in BSplineInterpolateImageFunction<br>
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<p class="MsoNormal">Dear all,</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">The BSplineInterpolateImageFunction class has two functions to compute<br>
the derivative:<br>
- EvaluateDerivativeAtContinuousIndex<br>
- EvaluateValueAndDerivativeAtContinuousIndex</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.</p>
<p class="MsoNormal">I believe this bug was introduced a long time ago by commit 6abbc7969a90786c4c73f5d191f634db536c2d1d :</p>
<p class="MsoNormal"> </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></p>
<p class="MsoNormal"> </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:</p>
<p class="MsoNormal">(-0, 7.48376e-009, -1, 7.48376e-009, 1, 7.48376e-009, 1, -7.48376e-009, 0)</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Current output:</p>
<p class="MsoNormal">EvaluateDerivative: [42.7697, -9.97885, 22.2913]</p>
<p class="MsoNormal">EvaluateValueAndDerivative: [-22.2913, -9.97885, 42.7697]</p>
<p class="MsoNormal">But that should really be the same. Note that the first and third entry are switched, and negated.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">I filed a gerrit entry which proposes a fix:</p>
<p class="MsoNormal"><a href="http://review.source.kitware.com/#/c/11016/">http://review.source.kitware.com/#/c/11016/</a></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">After that fix the output is as follows:</p>
<p class="MsoNormal">EvaluateDerivative: [42.7697, -9.97885, 22.2913]</p>
<p class="MsoNormal">EvaluateValueAndDerivative: [42.7697, -9.97885, 22.2913]</p>
<p class="MsoNormal">So, equal as it should be.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Looking forward to your feedback,</p>
<p class="MsoNormal">Regards, Marius</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span lang="EN-GB">Marius Staring, PhD</span></p>
<p class="MsoNormal"><span lang="EN-GB">Division of Image Processing (LKEB)</span></p>
<p class="MsoNormal"><span lang="EN-GB">Department of Radiology</span></p>
<p class="MsoNormal"><span lang="EN-GB">Leiden University Medical Center</span></p>
<p class="MsoNormal"><span lang="EN-GB">PO Box 9600, 2300 RC Leiden, The Netherlands</span></p>
<p class="MsoNormal"><span lang="EN-GB">phone: +31 (0)71 526 2137, fax: +31 (0)71 524 8256</span></p>
<p class="MsoNormal"><span lang="EN-GB"><a href="mailto:m.staring@lumc.nl">m.staring@lumc.nl</a></span></p>
<p class="MsoNormal"> </p>
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