Hemisphere GPS 874-0004-000 User manual
Hemisphere GPS
RTK Rover Workflow for Crescent Based Receivers p/n 874-0004-000
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RTK Rover Workflow for Crescent Based
Receivers
Part Number 874-0004-000 Released August 27, 2010
IʼMAN EXPERT:
•Power on
•Provide corrections to any receiver port in DFX format.
•The GPGGA and GPGST messages will show the RTK rover solution and accuracy,
respectively
IʼMA NOVICE:
A. Apply power to the receiver
B. Check $JAPP to ensure RTK application is running
C. Check $JK to ensure the subscription code is ready to work as an RTK rover (3008 or
Higher)
D. Ensure the corrections are being received on a receiver port in either DFX format at the
correct baud rate
E. Monitor the quality indicator, correction age, and reference station ID number in the
GPGGA message for performance. Monitor the standard deviations of latitude, longitude,
and height from the GPGST message to determine positioning accuracy.
WALK ME THROUGH IT SLOWLY:
1. Place the GPS antenna outside in an open area where it will be able to track as many
satellites as possible.
2. Connect the antenna to the antenna cable, and then connect the cable to the receiver.
3. Apply power to the receiver.
4. Connect your PC COM port to the receiverʼsport. Port A will be used in this workflow.
5. Select software to communicate with the Crescent based receiver. SLXmonDF or
HyperTerminal can be used, along with other choices. If you have trouble connecting,
ensure you are selecting the right port and baud rate, and ensure the correct cables are
connected properly.
6. Once connected, from a screen that allows commands to be sent to the receiver, send a
$JAPP command. The response may be like this:
Hemisphere GPS
RTK Rover Workflow for Crescent Based Receivers p/n 874-0004-000
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$>JAPP,LOCRTK,AUTODIFF,1,2
The important item is that LOCRTK appears immediately after $JAPP. If the word
LOCRTK is in the text but not as the first application (see below), you will have to switch
applications inside the receiver:
$>JAPP,AUTODIFF,LOCRTK,2,1
To switch applications, issue $JAPP,OTHER to the receiver and it will reboot in the new
application. You may need to reconnect your PC software once this happens.
If the LOCRTK application is not installed on the receiver, you will have to do that before
you can have it work as an RTK rover. Consult your dealer or Hemisphere GNSS
Technical Support for more details.
7. Once you have confirmed the LOCRTK application is active, issue a $JK command to
ensure the subscription code is ready to work as an RTK rover. The response will be
something like this:
$>JK,01/01/3004,04
The number 3004 here is important. This is the subscription code. If the code is 3004,
3005, 3008, or 3009, the receiver will be able to work as an RTK rover. If the number is
not one of these two values, contact your dealer or Hemisphere GNSS Technical
Support. They will need to have all of the information from the response to the $JI
command. For example:
$>JI,1800072,1,7,30062008,01/01/1900,01/01/3000,1.5L,46
8. Once you have confirmed that the subscription code is capable of working as an RTK
rover, you are ready to start receiving corrections on one of the ports. This workflow will
use Port B for receiving corrections.
9. Ensure your corrections port is set to the correct baud rate. You can use $JSHOW to
verify what it is currently set to, or you can just re-define it as needed. For example,
assuming you are connected to Port A through your software, issue
$JBAUD,9600,OTHER to set Port B to 9600 baud.
10. Typically corrections are transmitted over a radio modem link from the base to the rover.
Ensure the rover radio modem device is set to the correct baud rate and is ready to
receive corrections. Ensure the radio antenna is connected properly and is located in an
appropriate location. Apply power to the radio modem. Connect the radio modem data
port to the GPS receiverʼscorrection port (Port B for this workflow).
11. The RTK corrections are in a certain format. The receiver accepts DFX correction
formats. Use DFX format (Hemisphere GNSS proprietary) for the highest performance
of your RTK system – it is best suited for use with all Hemisphere GNSS equipment.
The Crescent RTK rover will automatically sense which correction format is being
received and will start functioning as an RTK rover.
12. You can issue the $JASC,GPGGA,1 and $JASC,GPGST,1 commands to watch the
performance and accuracy of the RTK rover.
Hemisphere GPS
RTK Rover Workflow for Crescent Based Receivers p/n 874-0004-000
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Watch the quality indicator, correction age, and reference station ID number in the
GPGGA message for RTK performance. The quality indicator will be 4 when RTK is
working properly. The quality indicator will be 2 when in L-DIF mode. You should
check the correction age to ensure the radio modem link is receiving corrections
consistently. If it is 1 then no corrections have come through and you should ensure
the baud rates are correct at the rover GPS receiver, rover radio modem, base radio
modem, and base GPS receiver. The correction age should be 1, representing 1
second of delay since the last correction was received – this should be steady at 1 if
your radio modem link is working properly. If it starts counting up, your link is not stable.
The reference station ID number will indicate the identification number of the base
station that is being used. If it is blank, then you likely have not received any corrections
yet and you should check the radio link.
Watch the standard deviations of latitude, longitude, and height from the GPGST
message to determine positioning accuracy. They are in meters. Under proper RTK
operation, the values should be around 0.010m, representing centimeter level accuracy.
NOTES ON RTK ROVER OPERATION:
Your Hemisphere GNSS RTK rover receiver can provide information about the base station.
Issue $JRTK,17 to see the latitude, longitude, and height, of the base station. You can also
display the distance to the base station (in meters) by issuing the $JRTK,18 command.
FURTHER INFORMATION:
Consult www.HemisphereGNSS.com for the latest information, or contact your dealer.
For support via email, please contact TechSupport@HemisphereGNSS.com
This document is provided for technical support purposes only. Please refer to the product documentation for
warranty, license and safety information associated with the product.
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