Time format and absolute time when exporting data

[turboscholz]

yes, there is a time stamp associated to the location, however, it is just an estimate (or vice versa: the location is an estimate for the time stamp). There is definitely an associated uncertainty (IIRC, Android even provides a 1σ interval). This time stamp is in fact already used to sync the location signal to the running time of experiments.

To be on the safe side I am just repeating what you said with my own words: By measuring the GPS coordinates you can retrieve the absolute time stamp of the GPS signal, and with that one you can than align the GPS coordinates to the relative time stamp of the experiment.

Wouldn't it be possible to export the measured absolute time stamp of the GPS signal in a separate column in the Location.csv file? This would be totally sufficient for my special use case. I could compare this absolute time with the time stamp and the coordinates of an external GPS device. This means that there is no need to export all experiments with an absolute time stamp.

Yes, the GPS data also provides the uncertainty for the horizontal and vertical location, that's really nice. Unfortunately, I see a systematic shift of the gully cover locations found in my data analysis compared to their real locations, which makes me wonder if something is not correct in the overall approach: The found location on the map is most of the time like 3-5 meters behind the real position.

Just speculating:

1. Maybe there is an issue in the beginning of the experiment where it always takes some time to retrieve the first data points from enough GPS satellites to calculate the current location of the smartphone. At the same time, the acceleration sensor is already read out from the start. Can the shift I was talking about can come from this time frame in the beginning of the measurement?
   
2. What about time difference (of some seconds) between the absolute time stamp of the GPS signal and the absolute time of the smartphone? Is there a relation which could come into play? I mean, how is the relative time difference between the start of the experiment and the GPS time stamp calculated. I speculate that you somehow must take the absolute time of the smartphone into account, which might be running some seconds off compared to the GPS signal.