I receive a CMLogItem from a CoreMotion query in swift (could be accelerometer, gyroscope). Now, I want to get the timestamp of that sample, preferably as a Date() object. CMLogItems have a property .timestamp of type TimeInterval.
The documentation tells me the following:
The CMLogItem class defines a read-only timestamp property that records the time a motion-event measurement was taken.
However, I am not sure how to convert this timestamp to a Date() object because I dont know what the timestamp is referring to.
Another documentation says:
The timestamp is the amount of time in seconds since the device booted.
But this seems really weird and I dont understand why apple would create such an inconsistent and complicated API.
Proper answer is:
extension CMLogItem {
static let bootTime = Date(timeIntervalSinceNow: -ProcessInfo.processInfo.systemUptime)
func startTime() -> Date {
return CMLogItem.bootTime.addingTimeInterval(self.timestamp)
}
}
This gives us stable, monotonic results, which is not a case, when bootTime is computed every time startTime is called.