B Spline interpolation is broken for some documents.
Open the test document attached to Bug 47632 and switch to edit mode. Somewhere in Splines.cxx must be an error implementing the algorithm mentioned in ODF 1.2.
Algorithm is implemented in chart2/source/view/charttypes/Splines.cxx
This one is getting really nasty. I have more or less implemented the algorithm totally new and added unit tests but the algorithm results in memory corruption.
Have to spend some time on other calc bugs.
Created attachment 59314 [details]
File for experiments
Hi Markus. I think, that the problem is caused by identical y-values. When you increase the x- or y-values step by step, you can notice, that the amplitude of the curves increases too. I tend to think, that this cannot be avoided, because B-Spline interpolation curves are parametric. I guess, that it is a property of this kind of interpolation.
When you agree to that and not find an error in the algorithm, I suggest, that we implement some functional interpolation. For those of cause the x-values have to be sorted as it has been in older versions of OOo. Perhaps we can discuss this on the Hackfest?
I don't think that the B-Spline algorithm itself has a problem with identical y values. I fear more that one of our assumptions in the implementation is wrong.
I think I remember from my Numerical Math 2 lecture that there is no such limitation for B splines but I would need to check with my script.
I have now to fix some more calc bugs before I can come back to this problem but I will finally try to run this data through MATLAB and compare the result of each individual step with the MATLAB result.
I already did that for the creation of t and u with my reworked implementation and they were the same in matlab and in my implementation. I will try to get the splitted up implementation into master before the hackfest and hopefully the test data ready until then.
Sadly we are not free to implement another algorithm because ODF1.2 explicitly mentions this algorithm. Nevertheless if there is really a problem with the ODF algorithm we may talk to Kohei/Thorsten how to proceed.
*** Bug 57234 has been marked as a duplicate of this bug. ***
Is there any development in working on this bug or should it be unassigned? Last comment is from 2012.
This bug has been in ASSIGNED status for more than 3 months without any activity. Resetting it to NEW.
Please assigned it back to yourself if you're still working on this.
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