Velodyne HDL-64E S3 - Packet Format and Status Byte for GPS Time Stamping; Timestamp Accuracy Rules and Accuracy

HDL-64E S3
High Definition LiDAR Sensor
Page 19
Velodyne LiDAR, Inc.
©
2019
63-HDL64ES3 REV K
Packet Format and Status Byte for GPS Time Stamping
The 6 bytes at the end of the data packet report GPS timing and synchronization data. For every packet,
the last 6 bytes are formatted as follows:
Timestamp Bytes in Reverse Order in microseconds
Bytes Description Notes
4
GPS
timestamp
32 bit unsigned integer timestamp. This value represents microseconds from
the top of the hour to the first laser firing in the packet.
1
Status
Type
8 bit ASCII status character as described in Appendix E. The status byte
rotates through many kinds of sensor information.
1
Status
Value
8 bit data as described in Appendix E.
Within the GPS status byte, there are 4 GPS status indicators:
. 0: No GPS connection.
. A: Both PPS (synch) and GPS command have signal.
. V: Only GPS command signal, no PPS (synch).
. P: Only PPS (synch) signal, no GPS time command.
Timestamp Accuracy Rules and Accuracy
The following rules and subsequent accuracy apply for GPS timestamps:
GPS Connection Timestamp Info Accuracy Notes
GPS isn’t
connected (GPS
Status 0)
The sensor starts running on
its own clock starting at
midnight Jan 1 2000. This
date and time data is
reflected in the H, M, S, D,
N, and Y data values.
Expect a drift of about 5
seconds/day.
The sensor clock
does not correct for
leap years. See
Appendix E for more
information.
GPS is connected
The H, M, S, D, N, and Y
data values are obtained
from the $GPRMC NMEA
record.
GPS time synching runs in
one of two modes:
. The GPS is used first.
The accuracy is of the
GPS device employed.
. When the GPS
achieves
lock, the
sensor clock is then
within +/-50µs of the
correct time at all times.
GPS is
disconnected
after being
connected
The sensor continues to run
on its own clock.
Expect drift of about 5
seconds/day