Introduction to RTK Data Processing
How to get centimeter level accuracy?
Part - 1
13 February 2024
Kaito Kobayashi, Tomohiro Ozeki, Nobuaki Kubo
Tokyo University of Marine Science and Technology

TUMSAT GNSS Lab

1Contents
1.

What is RTK2.

RTK applications

3.

How to build RTK environment
1.

2.

4.

Base-Station
1.

Receiver and Antenna types

2.

How to setup base-station

Rover Unit
1.

Receiver and Antenna Types

2.

How to setup rover

Data Recording and Format Conversion for RTK
1.

SBF, UBX, JPX etc. to RINEX

2.

Which version of RINEX shall be used?

TUMSAT GNSS Lab2

1. What is RTK
RTK is high accuracy positioning method using “Base Station”.

Knownposition

Antenna
mm level Baseline vector
Antenna

Observation data
ReceiverInternetUHF,VHF

ReceiverBase Station

UserPosition

Rover
TUMSAT GNSS Lab

31. What is RTK
If “Base station” is not fixed → Moving-base RTK
You can get precise relative position, angle between 2 antenna.

Phase Difference②

Phase Difference①

Baseline vector(Relative position)TUMSAT GNSS Lab

42. RTK applications
RTK can expand GNSS use field over traditional PNT (Positioning, Navigation, Timing).

TUMSAT GNSS Lab

52. RTK applications
RTK◆Construction

RTK survey
andUAV mapping

Traditional optical survey
RTKMoving-base
RTK

Machine control
using 3D dataandAttitude monitoring

Complex machine control
TUMSAT GNSS Lab

62. RTK applications◆ITS (Intelligent Transportation System)

RTK

SPP

Auto driving support
Car navigation

RTK
Moving-base
RTK

Road pricing by lane

Distance control
TUMSAT GNSS Lab

72. RTK applications◆Maritime

RTK
Moving-base
RTK

SPP

Seabed survey

RTK

Ship navigation

Moving-base
RTK

RTK
Moving-base
RTKAuto berthing

Drilling, Maritime construction
TUMSAT GNSS Lab8

2. RTK applications◆UAVMoving-base
RTKSPP

AttitudeMonitoringMoreprecise map

RTKRTKMapping

RTK Drone
TUMSAT GNSS Lab

Distributed type
Ground Control Point
92. RTK applications
Agriculture Machinery Guidance◆Agriculture

RTK-RTKSPP

Shift to young generation
Effective working

TUMSAT GNSS Lab10

3. How to build RTK environment◆Base station overview
I explain the most common broadcast way using “Ntrip server”.
However you can also use VHF/UHF radio, Bluetooth, LAN or cable communication to broadcast base station data.
Antenna

ReceiverAntenna

Rover (User)

Receiver

PCInternet

Ntrip
castersoftware

Ntrip
serverAntenna

ReceiverRover (User)
Antenna

ReceiverRover (User)TUMSAT GNSS Lab

11

3. How to build RTK environment◆Base station antenna
Install antenna in open sky & static environment.

Japanese government base station

Our University base stationTUMSAT GNSS Lab

Temporary base station

12

3. How to build RTK environment◆Base station receiver selection
The receiver should support raw data output.
• RTCM3
Standard format for RTK. Select base station
position and observation message is must.
• Receiver manufacturer format
Binary message.
Input support is depend on the rover receiver.

https://www.use-snip.com/kb/knowledge-base/an-rtcm-message-cheat-sheet/

TUMSAT GNSS Lab

13

3. How to build RTK environment◆Base station receiver setting
Change receiver configuration to output RTCM message from USB port.
Here I will show example using u-blox F9P.

TUMSAT GNSS Lab14

3. How to build RTK environment◆Base station antenna position
You need to know your base station antenna position with cm level accuracy.
・RTKIf there is another RTK base station near your base, you can calculate by PPK (Post-ProcessKinematic).
AntennaFree RTK base stations.
-IGS station http://www.igs.org/network
datalink : ftp://cddis.gsfc.nasa.gov/gnss/data/daily-Local CORS https://www.chcthailand.com/cors-picture

Don’t over
40km distance

ReceiverYour base station

Rinex data

Nearest basestation

PPK byRTKLIBTUMSAT GNSS Lab15

3. How to build RTK environment◆Base station antenna position
You need to know your base station antenna position with cm level accuracy.
・PPP
If there is no another RTK base station, calculate by PPP.

Antenna

IGS product.sp3 & .clk data

Free PPP service- RTKLIB with IGS product (http://www.rtklib.com/)- Net_Diff with IGS product (https://github.com/YizeZhang/Net_Diff)- Trimble RTX (https://www.trimblertx.com/UploadForm.aspx)- CSRS-PPP (https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php)- MADOCA-PPP

ReceiverRinex data

PPP byRTKLIB/Net_DifforSubmit Rinex data

PPP byRTKLIB/NetDiff

IGS product : (http://mgex.igs.org/IGS_MGEX_Products.php)
TUMSAT GNSS Lab163. How to build RTK environment◆Base station antenna position
Sample of PPP solution

Net_Diff + MGEX productUse this position as your base station position.
TUMSAT GNSS Lab

Trimble RTX service173. How to build RTK environment◆Base station antenna position
Unless there is a special reason, I don’t recommend to use optical survey position or SPP average
position for the base station position.
Traditional optical survey

Bias of SPP

Local survey coordinate has a gap
with GNSS coordinate (ITRF).

TUMSAT GNSS Lab18

3. How to build RTK environment◆Push out data to Ntrip server
You can check your Mount Point from “NTRIP Browser” in RTKLIB.

Your base station addressTUMSAT GNSS Lab

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3. How to build RTK environment◆RTK (Septentrio with PC)

Select base station

Input to COM17 port

Use Ntrip client function of “Data Link”
in “RxTools”
https://www.septentrio.com/en/products/software/rxtools
Downloand link
https://www.septentrio.com/en/support/software/rxtools

2 COM port
TUMSAT GNSS Lab20

3. How to build RTK environment◆RTK (ublox with PC)
Use Ntrip client setting in u-center.
https://www.u-blox.com/en/product/u-center

NTRIP client setting
Receiver>NTRIP Client
Select mount point and click“OK”.

RTK support is M8P and F9P

TUMSAT GNSS Lab21

3. How to build RTK environment◆RTK (RTKNAVI)Real time RTK engine that supports many receivers.
To use RTKNAVI, first you should set receiver to output “raw data”.
“raw data” means binary observation message include RTCM.
RTKNAVI decodes this “raw data” and calculate RTK solution.
Here, I show the example using u-blox receiver.

Supported “raw data” formats
TUMSAT GNSS Lab22

3. How to build RTK environment◆RTK (RTKNAVI)
Receiver configuration on u-center.
First, select COM port of the receiver and connect. Then open “message view”.
Open message viewDevice Manager

Select port

Receiver COM port
TUMSAT GNSS Lab23

3. How to build RTK environment◆RTK (RTKNAVI)
Receiver configuration on u-center. Open message view from View>Message View.
You need to click “send” after change configuration.

Right click -> “Enable”
Click “Send”
Enable output of RAWX & SFRBX (UBX-RXM )Setting to output UBX format (UBX-CFG-PRT)TUMSAT GNSS Lab243. How to build RTK environment◆RTK (RTKNAVI)
After receiver configuration was completed, save it and disconnect receiver.

“Disconnect”

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3. How to build RTK environment◆RTK (RTKNAVI)Open RTKNAVI.

TUMSAT GNSS Lab26

3. How to build RTK environment◆RTK (RTKNAVI)
Set input stream.

Select Ntrip mount pointTUMSAT GNSS Lab27

3. How to build RTK environment◆RTK (RTKNAVI)
Set output stream & log stream.

Here the RTK position will be written to the file.
Also you can choose other option (TCP, Serial) according
to your use caseTUMSAT GNSS Lab28

3. How to build RTK environment◆RTK (RTKNAVI)
Set option to calculate RTK.
After option setting, click“Start” and then RTK starts.

TUMSAT GNSS Lab

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4. Data Recording and Format Conversion for RTK◆RTK post processing need GNSS raw data.
◆After changed the configuration of the receiver to output raw observation, you need to record
it.
◆Most of the receivers output its data stream by serial communication.
◆Easy way to record the data on PC is use RTKLIB.
PCReceiver

Serial communicationRTKLIBSTRSVR
xxx.ubx

TUMSAT GNSS Lab

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4. Data Recording and Format Conversion for RTK◆Data recording (STRSVR)

Start recording

File name Tips
TUMSAT GNSS Lab

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4. Data Recording and Format Conversion for RTK◆GNSS raw data is normally original binary format by receiver manufacturer.
◆To use raw data on third party RTK software, we need to convert it to RINEX format.
◆About RINEX format > https://www.igs.org/wg/rinex/◆RTKCONV on RTKLIB can convert several manufacturer’s receiver data.
xxx.ubx

original format (Binary)xxx.obs

TUMSAT GNSS LabRINEX format (ASCII)

32

4. Data Recording and Format Conversion for RTK◆Data conversion (RTKCONV)GNSS raw data
Select receiver manufacturer.obs is observation file with RINEX format.nav is ephemeris file with RINEX format

TUMSAT GNSS Lab

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4. Data Recording and Format Conversion for RTK
Output RINEX version.
Recommend upper 3.02

◆Data conversion (RTKCONV)

Recommend check“Scan Obs Types”
Satellite constellations
you want to output

Recommend check all
C: Code range
L: Carrier phase
D: Doppler shiftS: SNRStart conversion

TUMSAT GNSS Lab

GNSS frequencies you want to use
Recommend check all for general purpose

34

4. Data Recording and Format Conversion for RTK◆Data conversion (RTKCONV)
After conversion you can find .obs file and .nav file which can open with text editor.

TUMSAT GNSS Lab

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4. Data Recording and Format Conversion for RTK◆Data conversion (RTKCONV)You can also check RINEX format data graphicallyby RTKPLOT.
Satellite sky plot

SNRElevationTUMSAT GNSS Lab36

7. Useful web sites◆Useful web sites for your RTK experiment• http://www.denshi.e.kaiyodai.ac.jp/gnss_tutor/base_station.html• https://home.csis.u-tokyo.ac.jp/~dinesh/• http://www.rtklib.com/TUMSAT GNSS Lab37