Filter data that is not sampled uniformly?

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Hi, does anyone know how to filter data that's not sampled at a constant frequency? The data is based on pressure-crank angle, so I have a pressure sample at every 0.1 crank angle degree.
I'm trying to the use butter() function, but it requires a sampling frequency...
Regards, TheNovice
  4 Comments
dpb
dpb on 1 Mar 2015
Is there a recorded timing interval or other way to know rpm, I presume? If so you can derive time. I'll have to cogitate on w/o a little...
TheNovice
TheNovice on 1 Mar 2015
Edited: TheNovice on 1 Mar 2015
I have an average rpm of 1000 in the attached sample. So yeah, I can reconstruct a time vector with uniform distribution from that. The problem I see though is that the RPM is not constant during a cycle, and this approach will contribute to an error. The question is how large...

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Accepted Answer

Star Strider
Star Strider on 1 Mar 2015
I have no mechanical engineering background, so I’m having a difficult time imaging what your data actually are. If it is constantly sampled, you could filter them with respect to the crank angle, or interpolate (resample) them at a constant sampling frequency in time. I have no idea how valid this may be, since I don’t have your data.
  9 Comments
TheNovice
TheNovice on 1 Mar 2015
Edited: TheNovice on 1 Mar 2015
Thank you the very informative answer. You have a lot of good points that I will consider in the future. Also a thank you for the suggested books, will definitely look into them. This is an area I need more knowledge of.
Thank you again for your help!
Regards, TheNovice
Star Strider
Star Strider on 1 Mar 2015
My pleasure!
From my own experience, I would take courses on digital signal processing, experiment design, mathematical modeling and nonlinear parameter estimation, and if you are going to do a significant amount of instrumentation design, a course in hardware design and hardware signal processing. If you are doing imaging in your research, a course in digital image processing would also be necessary.
Your research seems interesting. Have fun!

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