This article provides a detailed overview of the Astroskin CSV file format. It explains the structure and contents of these files, including the timestamp information and the various data channels that are recorded.
You’ve downloaded the CSV data file for your Astroskin record or activity and you’re wondering what each column stands for (for more details, please also refer to the API documentation):
Timestamps
1st column: time [s/1000]
The Astroskin timestamps in the CSV format file are in 1000ths of a second (i.e. time [s/1000]).
The timestamps are in Unix epoch time format, which corresponds to the number of seconds that have elapsed since January 1st, 1970 at 00:00:00 GMT With Astroskin, the Timestamps are also multiplied by a 1000. Each timestamp in this format contains the Date and Time.
To convert these timestamps into real-time:
1. Divide the “time” value by 1000
1.69137E+12 = 1691371518000
1691371518000 / 1000 = 1691371518
2. Convert the resulting number using an epoch & unix converter.
1691371518 = Monday, August 7, 2023 1:25:18 AM GMT
1 Hz Data Channels
The data channels highlighted in orange in the image are recorded at a predefined frequency of 1 Hz, meaning they provide one data point per second.
2nd column: Breathing Rate (respirations/minute, rpm)
This is the number of breaths per minute, calculated as the average breathing rate of the last 7 breaths.
3rd column: SPO2 (percent, %)
Oxygen saturation level as returned by A Nonin optic sensor.
5th column: Minute Ventilation (milliliters per minute, mL/min)
This is the volume (in mL) of breathed air per minute, calculated for the last 7 complete respiration cycles.
6th column: Systolic Pressure (mmHg)
Systolic blood pressure: Blood pressure derived from the PTT value.
8th column: Activity (g)
Signal based on the accelerometer intensity vector. Basically, we get a square root of the sum of the square of each of the accelerometer components.
9th column: Heart Rate (beats per minute, bpm)
This is the heart rate in beats per minute, calculated as the average of the last 16 heartbeats.
10th column: Cadence (steps per minute, spm)
Cadence: Averaged over the last 7 strides based on the accelerometer.
Asynchronous Data Channels
The data channels highlighted in blue in the image below are recorded at an asynchronous frequency. This means that each data point is reported at the specific timestamp when the event occurred, rather than being sampled at a predetermined, regular interval.
4th column: PTT (seconds, s)
Pulse transit time: Time difference between the Nonin PPG digital output and the QRS.
Note: The Nonin PPG digital output is delayed by 172 ms. The time and value of the PTT should be reduce by 172 ms to obtain the value at 50% of the PPG signal.
7th column: Sleep Position
This is the user's sleep position during a sleep activity. Sleep positions detected are belly (1), back (2), right (3), left (4) and standing (5).
The sleep positions are defined when the device is placed in the pocket with bluetooth led pointing downward, the leds pointing outside and the device on the side of the body.