plot_wfdb() times don't math for annotation and record

[elliot-brown]

The following code either has the annotations in the incorrect place or results in an IndexError, depending on the specific choices of sampfrom and sampto:

record = wfdb.rdrecord('mitdb/100', sampfrom=360, sampto=1080)    
annotation = wfdb.rdann('mitdb/100', 'atr', sampfrom=360, sampto=1080)
wfdb.plot_wfdb(record=record, annotation=annotation, time_units='seconds')

I believe the issue is that when plotting the record only, the x-axis begins at 0 regardless. But the x-axis of the annotation-only plot begins at the corresponding time. In this example,

wfdb.plot_wfdb(record=record, annotation=None, time_units='seconds')

plots from 0 to 2 seconds, whereas

wfdb.plot_wfdb(record=None, annotation=annotation, time_units='seconds')

plots from 1 to 3 seconds.

So when trying to plot both,

wfdb.plot_wfdb(record=record, annotation=annotation, time_units='seconds')

you typically get an IndexError (because the annotation index in out of bounds) or sometimes a graph with annotations that don't line up.

I'm not sure what the best solution is. It makes sense that the annotations are associated with a sample number. Maybe the record should be too?

[Lucas-Mc]

Hey @elliot-brown, I am going to try and work on this now. I have the following plot to share:

This is what it looks like if you remove the final annotation generating the error, confirming your suspicions about mis-aligned indexing. Code to duplicate:

import wfdb
import numpy as np
record = wfdb.rdrecord('mitdb/100', sampfrom=360, sampto=1080)    
annotation = wfdb.rdann('mitdb/100', 'atr', sampfrom=360, sampto=1080)
annotation.sample = np.array([370,662])
annotation.subtype = np.array([0,0])
annotation.chan = np.array([0,0])
annotation.num = np.array([0,0])
annotation.aux_note = np.array(['',''])
wfdb.plot_wfdb(record=record, annotation=annotation, time_units='seconds')

[Lucas-Mc]

Update: The code works if you make the following edit:
annotation = wfdb.rdann('mitdb/100', 'atr', sampfrom=360, sampto=1080, shift_samps=True)
This then generates the following correct plot:

It appears like the annotations aren't being shifted over unless the shift_samps parameter is set to True although it should if the sampfrom is greater than 0 and the record is being plotted with it. Working on how to find the best solution.

[Lucas-Mc]

I'm making a pull request now and decided to leave the functionality as it is but add a more descriptive error message in place of the current IndexError default message. Instead, I specifically tell the user to utilize the shift_samps=True parameter when importing the annotation data. Hopefully this helps!