IIR filter triggers a resample even if file is uniformly sampled

[tkevinbest]

When selecting "filter input coordinates" in the ID tool, my IK data gets resampled even though it was output at a fixed frequency from the IK tool. The code here says it should only resample if the sampling is not uniform:

opensim-core/OpenSim/Common/Storage.cpp

Line 2370 in cbf9c74

if(dtmin<SimTK::Eps) {

. There appears to be something wrong with the machine precision check and determining whether or not the sampling is uniform.

I know that my data was resampled because it is a very long file, beyond the max size of the resampling function and thus my sampling rate drops substantially when resampling.

Version 4.5-2024-01-10-3b63585

[nickbianco]

@tkevinbest, thanks for reporting this issue. Would you mind posting a sample data file so we can create a minimum working example?

[tkevinbest]

The file is too big to upload, but I've shared it here: https://www.dropbox.com/scl/fi/7q9lcho6imbx7mbypurne/OpensimResampleTestCase.zip?rlkey=ajt3fxqzzw7w4t4ra31qq08hd&st=7x6w9uks&dl=0

[mrrezaie]

Hi @nickbianco, just wanted to say that I tested the files and received two warnings in addition to the machine precision check reported by @tkevinbest:

• [warning] Storage.resample: resampling at time step 0.0916798 (but minimum time step is 0.00400000).
  For some reasons, a limitation has been set on data size in both resample and resampleLinear methods:
  

  opensim-core/OpenSim/Common/Storage.cpp

  Line 118 in 897689f

  const int Storage::MAX_RESAMPLE_SIZE = 100000;

  
  

  opensim-core/OpenSim/Common/Storage.cpp

  Lines 2525 to 2528 in 897689f

  	// Limit aDT based on expected number of samples
  	int maxSamples = MAX_RESAMPLE_SIZE;
  	if((getLastTime()-getFirstTime())/aDT > maxSamples) {
  	double newDT = (getLastTime()-getFirstTime())/maxSamples;

• [warning] Cutoff frequency should be less than half sample frequency. Changing the cutoff frequency to 0.49*(Sample Frequency)...cutoff = 5.34469
  This is probably a consequence of the above limitation (sample frequency is changed).

Hope this helps.