Time error when using filter coordinates (Analyse tool)

[Yanran Jiang]

Hi there,

I encounter a time error when filter the coordinates (Analyse tool). The original time should be from 0 to 1012.18, but the filter function resample the time, leading to executing time from -0.02 to 1012.18. Is there any solution to start with 0 rather than -0.02?

Thanks,
Yanran

[Dimitar Stanev]

Hi Yanran,

This is because if you want to calculate high order derivatives for t = 0 using finite difference the internal calculations need at least two more points before and after t = 0. If you want to start at t = 0 then you initial time could be something like t = 0.02. Please note that if you filter your kinematics for 1000s it will take a lot of time to execute the analysis. Maybe a better approach is to restrict to a couple of seconds.

[Yanran Jiang]

Hi Dimitar,

Thank you for your reply. I want to get velocity by using different subjects' marker motion data. When I scale, IK and run analyse tool for the first subject, the time starts from t=0s with loss pass filter. But I do the totally same procedure for the second and third subject, the initial time changes from t=0s to t=-0.0025. That's wired to me. Also, I found when the initial time is t=-0.0025s, the time step also changes from 0.01s to around 0.02s. I try to change my initial time as 0.0025s but it doesn't help. Do you have any suggestions?

Best,
Yanran