../_config.adoc = Timestamps
Simulation time refers to the timestamp within a simulation environment.
Definition of zero time of simulation time - Zero time is arbitrary but must be identical for all frames and corresponding messages (probably within one simulation). - Zero time does not need to coincide with the unix epoch. - It is recommended to use the start time of the simulation as zero time.
SensorData-specific timestamp - Point in time that the sensor data message becomes available to the rest of the system (i.e. the driving functions). - Corresponds with the sending time / publish time. - Takes into account internal sensor processing latency. - Does not include bus communication delays (e.g. latency) that occur after the sensor output.
HostVehicleData-specific timestamp - Time at which the host vehicle data message becomes available as a snapshot of the on-board network information.
Other top-level message timestamps - GroundTruth, SensorView, TrafficCommand, TrafficUpdate, TrafficCommandUpdate, StreamingUpdate - The Timestamp coincides both with the notional simulation time the data applies to and with the time it was sent / published. - No inherent latency for the corresponding data, as opposed to e.g. SensorData-specific timestamp.
The definition of vehicle-global synchronized time originates from ISO 23150. The corresponding definition applies to the following types of OSI timestamps.
Measurement time
- Used in:
- DetectedEntityHeader/measurement_time (time at which the measurement was taken)
- SensorDetectionHeader/measurement_time (time at which the measurement was taken)
- last_measurement_time (time of last real-world measurement that the corresponding set of sensor data takes into account)
- DetectedItemHeader/age (amount of time that this detected object has been continuously observed/tracked; relative to measurement_time of DetectedEntityHeader)
- Time at which the actual measurement was taken in vehicle-global synchronized time.
- Usually corresponds to the timestamp of the GroundTruth that the sensor (model) processed to produce these results.
- Does not necessarily have to correspond with GroundTruth timestamp.
- Examples:
- For an ideal zero latency sensor model GroundTruth timestamp, SensorData timestamp and measurement time would be the same.
- For a sensor model that does not know its own internal latencies (e.g. dumb sensor with no internal time concept), measurement time and SensorData timestamp may be identical, but delayed from the GroundTruth timestamp.
Transformation / fusion time - Used in: - LogicalDetectionDataHeader/logical_detection_time - Timestamp at which the transformation and optional fusion was finished in the vehicle-global synchronized time.
SensorData system time - Internal time of modeled source of the sensor data. - Given as Unix timestamp. - Might not coincide with simulation time. - Example use cases: - Representation of real-world measurements and a corresponding sensor-internal timestamp - Simulation of time synchronization mechanisms/errors
EnvironmentalConditions/time_of_day - Time of day at host vehicle’s location
EnvironmentalConditions/unix_timestamp - Unix timestamp at host vehicle’s location