GPS/GNSS Synchronization Guide
For more information on how to physically connect a GPS to your Ouster sensor and synchronise the Ouster sensor timestamp to an NMEA sentence, please refer to your sensor’s Hardware User Manual.
Configuring the Ouster Sensor
Now that everything is configured and verified on the GPS side and you have connected everything to the Ouster sensor, it is time to configure the Ouster sensor to synchronize its timestamp with the GPS.
Set the
timestamp_mode
toTIME_FROM_SYNC_PULSE_IN
TCP command:
set_config_param timestamp_mode TIME_FROM_SYNC_PULSE_IN
Set the
multipurpose_io_mode
toINPUT_NMEA_UART
TCP command:
set_config_param multipurpose_io_mode INPUT_NMEA_UART
Set the polarity of the
sync_pulse_in
pin to match the GPS PPS polarity
TCP command:
set_config_param sync_pulse_in_polarity <ACTIVE_HIGH or ACTIVE_LOW>
Set the polarity of the
multipurpose_io
pin to match the GPS NMEA UART polarity
TCP command:
set_config_param nmea_in_polarity <ACTIVE_HIGH or ACTIVE_LOW>
Set the
nmea_baud_rate
to match the GPS NMEA baud rate
TCP command:
set_config_param nmea_baud_rate <BAUD_11520 or BAUD_9600>
Set the
nmea_leap_seconds
to match the current leap seconds as defined by TIA at this website, at time of writing this the leap seconds are37
TCP command:
set_config_param nmea_leap_seconds 37
Reinitialize and write the configuration
TCP command:
reinitialize
TCP command:
save_config_params
Checking for Sync
Once you have completed all the above you should be able to check for synchronization
Check the output from the TCP command:
get_time_info
Verify that the sensor is
locked
onto the PPS signal.
”sync_pulse_in”: { “locked”: 1 }
if not check the polarity and change it if necessary.
Verify that the sensor is
locked
on the NMEA signal.
“nmea”: { “locked”: 1 }
if not check the polarity and baud rate and change them if necessary.
Verify that
last_read_message
looks like a valid GPRMC sentence.
“decoding”: {“last_read_message”: “GPRMC,024041.00,A,5107.0017737,N,11402.3291611, W,0.080,323.3,020420,0.0,E,A*20”}
Verify that
timestamp
time has updated to a reasonable GPS time.
“timestamp”: {“time”: 1585881641.96139565999999, “mode”: “TIME_FROM_SYNC_PUSLE_IN”, “time_options”: { “sync_pulse_in”: 1585881641}}
Example output from get_time_info:
{
"timestamp":{
"time":1585881641.96139565999999,
"mode":"TIME_FROM_SYNC_PUSLE_IN",
"time_options":{
"sync_pulse_in":1585881641,
"internal_osc":302,
"ptp_1588":309
}
},
"sync_pulse_in":{
"locked":1,
"diagnostics":{
"last_period_nsec":10,
"count_unfiltered":832,
"count":832
},
"polarity":"ACTIVE_HIGH"
},
"multipurpose_io":{
"mode":"INPUT_NMEA_UART",
"sync_pulse_out":{
"pulse_width_ms":10,
"angle_deg":360,
"frequency_hz":1,
"polarity":"ACTIVE_HIGH"
},
"nmea":{
"locked":1,
"baud_rate":"BAUD_9600",
"diagnostics":{
"io_checks":{
"bit_count":2938457,
"bit_count_unfilterd":2938457,
"start_char_count":832,
"char_count":66526
},
"decoding":{
"last_read_message":"GPRMC,024041.00,A,5107.0017737,N,11402.3291611,W,
0.080,323.3,020420,0.0,E,A*20",
"date_decoded_count":832,
"not_valid_count":0,
"utc_decoded_count":832
}
},
"leap_seconds":37,
"ignore_valid_char":0,
"polarity":"ACTIVE_HIGH"
}
}
}