resampling by OMGUI

[vincentvanhees]

Following wadpac/GGIR#369 it may be good to also open an issue here.
It seems to me that something is wrong with the OMGUI resampling step.

What I did: I used OMGUI to export http://www.axivity.com/files/resources/longitudinal_data.zip twice to csv, once with resampling and once without resampling, and then plotted those signals on top of each other as a function of timestamp.

Next, I see a non-constant offset in the values between the types of output for all three axes. My guess is that this is related to the resampling because that is the only thing that changed.