<div dir="ltr">Thanks for clarifying this bug, bezier splines guarantee continuity with value at derivative. I look forward<div>to applying differentiable and continuous interpolation (with knot wise polarity) with this additional bug fix.</div>
<div><br></div><div>Best regards,</div><div>Cartik Sharma</div><div><a href="http://about.me/sharmacartik">http://about.me/sharmacartik</a></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, Apr 24, 2013 at 9:33 AM, <span dir="ltr"><<a href="mailto:M.Staring@lumc.nl" target="_blank">M.Staring@lumc.nl</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal">Dear all,<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">The BSplineInterpolateImageFunction class has two functions to compute<br>
the derivative:<br>
- EvaluateDerivativeAtContinuousIndex<br>
- EvaluateValueAndDerivativeAtContinuousIndex<u></u><u></u></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.<u></u><u></u></p>
<p class="MsoNormal">I believe this bug was introduced a long time ago by commit 6abbc7969a90786c4c73f5d191f634db536c2d1d :<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><a href="http://itk.org/gitweb?p=ITK.git;a=commitdiff;h=6abbc7969a90786c4c73f5d191f634db536c2d1d#patch13" target="_blank">http://itk.org/gitweb?p=ITK.git;a=commitdiff;h=6abbc7969a90786c4c73f5d191f634db536c2d1d#patch13</a><u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></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:<u></u><u></u></p>
<p class="MsoNormal">(-0, 7.48376e-009, -1, 7.48376e-009, 1, 7.48376e-009, 1, -7.48376e-009, 0)<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Current output:<u></u><u></u></p>
<p class="MsoNormal">EvaluateDerivative: [42.7697, -9.97885, 22.2913]<u></u><u></u></p>
<p class="MsoNormal">EvaluateValueAndDerivative: [-22.2913, -9.97885, 42.7697]<u></u><u></u></p>
<p class="MsoNormal">But that should really be the same. Note that the first and third entry are switched, and negated.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I filed a gerrit entry which proposes a fix:<u></u><u></u></p>
<p class="MsoNormal"><a href="http://review.source.kitware.com/#/c/11016/" target="_blank">http://review.source.kitware.com/#/c/11016/</a><u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">After that fix the output is as follows:<u></u><u></u></p>
<p class="MsoNormal">EvaluateDerivative: [42.7697, -9.97885, 22.2913]<u></u><u></u></p>
<p class="MsoNormal">EvaluateValueAndDerivative: [42.7697, -9.97885, 22.2913]<u></u><u></u></p>
<p class="MsoNormal">So, equal as it should be.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Looking forward to your feedback,<u></u><u></u></p>
<p class="MsoNormal">Regards, Marius<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><span lang="EN-GB">Marius Staring, PhD<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">Division of Image Processing (LKEB)<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">Department of Radiology<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">Leiden University Medical Center<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">PO Box 9600, 2300 RC Leiden, The Netherlands<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">phone: <a href="tel:%2B31%20%280%2971%20526%202137" value="+31715262137" target="_blank">+31 (0)71 526 2137</a>, fax: <a href="tel:%2B31%20%280%2971%20524%208256" value="+31715248256" target="_blank">+31 (0)71 524 8256</a><u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><a href="mailto:m.staring@lumc.nl" target="_blank">m.staring@lumc.nl</a><u></u><u></u></span></p>
<p class="MsoNormal"><u></u> <u></u></p>
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