Cropping continuous raw data does not update the measurement date

💬 Support & Discussions
1

Hi all,

I do not know if it is an intended behavior, but when we crop raw data, the measurement date of the mne.Info object is not updated, e.g. :

raw = mne.io.read_raw_fif("...")
cropped = raw.copy().crop(tmin=20) # in place operation : measurement time changes
cropped.info["meas_date"] == raw.info["meas_date"] # return True

In the above example, I would assume that cropped has a 20s later measurement date than raw, which does not seem to be the case. Is it an intended behavior ?

  • MNE version: 1.2.1
  • operating system: macOS 12.4
  • origin of raw data : from brainvision (the first marker in the .vmrk file contains the original measurement date)

Thank you,
Raphael

2

yes that is expected. It modified the raw.first_samp attribute that
gives you the delay between meas date and first data point

Alex

3

Thank you, I will go with raw.first_samp then.