Question
What time do the timestamp values describe? Is it the time the data is received? Is it the time the data is logged? Or does it describe something else?
Problem
I’m currently investigating the timestamps of some ULog files. For this i calculated the step sizes of the time_utc_usec and timestamp fields of the vehicle_gps_position.
I noticed a big jitter in the timestamp field and would like to know where this comes from.
Python code
from pyulog import ULog
import numpy as np
# Get ULog data
ulog = ULog('path/to/ulog/file')
gps_data = ulog.get_dataset("vehicle_gps_position")
# Extract data as numpy arrays
time_utc_usec = np.array(gps_data.data["time_utc_usec"])
timestamp = np.array(gps_data.data["timestamp"])
# Calculate step size between the two columns
time_utc_usec_steps = time_utc_usec[1:] - time_utc_usec[:-1]
timestamp_steps = timestamp[1:] - timestamp[:-1]