The IBI sequence provided by Empatica is obtained from an algorithm that already removes wrong peaks.
The picture below depicts a typical situation where the PPG data is corrupted by motion artefacts (graph a). The green points are the good heart beats, while the red x represent the wrong heart beats.
The wrong beats are not included in the IBI.csv and thus it may happen that two consecutive row in IBI.csv are not consistent with a standard tacogram. However the IBI.csv contains a timestamp indication since each row has the format : <time, distance>.
The graph b of the picture below indicates how each row is generated in the case of wrong heart beats. The latest two consecutive peaks at distance d1 are detected, and in t1 we add an IBI with value d1. In t2 other two consecutive beats are detected and thus we add a new ibi <t2, d2>. Since there have been a number of wrong heart beats, t2> t1+d1.
If you need to create a tacogram you could both use the time we provide or add a new row in the case t2> t1+d1 as explained in the picture
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