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GRTK User Manual

Statement:

The user using the GRTK centimeter-level positioning module is deemed to have automatically accepted this statement.

Please read this manual carefully before using the GRTK centimeter-level positioning module. If you have any questions you don't understand, please contact our technical support email info@blicube.com.

If you are interested with GRTK, welcome to join GRTK Discord Community to give us feedback.

Part 1 System Introduction

1.1 Introduction

GRTK is a dual-antenna high-precision differential positioning and directional module (Real Time Kinematics) independently developed by Blicube. A complete RTK system can be formed through two GRTK modules (one mobile terminal and one base station terminal).

The module is based on a new generation of high-performance GNSS SoC chip design (UM982 Inside), supports multi-system multi-frequency RTK positioning, dual-antenna high-precision orientation, GPS, GLONASS, Beidou, Galileo & QZSS navigation and positioning and heading with a compass inside. It is mainly for high-precision positioning and orientation requirements such as drones, robots and intelligent driving.

Figure 1.1 Physical image of GRTK centimeter-level positioning and orientation system

1.2 Parameters

  • Performance
Item
Frequencies BDS B1I/B2I1
GPS L1/L2
GLONASS L1/L2
Galileo E1/E5b
QZSS L1/L2
Single Point Positioning (RMS) Horizontal：1.5m
Vertical：2.5m
DGPS (RMS) Horizontal：0.4m
Vertical：0.8m
RTK (RMS) Horizontal：0.8cm+1ppm
Vertical：1.5cm+1ppm
Heading Accuracy (RMS) 0.1 degree/1 m baseline
Velocity Accuracy (RMS) 0.03 m/s
Time Accuracy (RMS) 20 ns
Time to First Fix (TTFF) Cold start < 25 s
Initialization Time < 5s (typical)
Reacquisition < 1 s
Correction RTCM v2.3/3.0/3.2
Data Output NMEA-0183
Update Rate 20 Hz
Inertial Navigation Accuracy < 5% of distance travelled during GPS denied conditions
Working Temperature -20℃ to +85℃
Power Supply 5v to 35v
Power Dissipation ~1W
Compass inside IST8310
  • Physical size

Figure 1.2 Schematic diagram of physical size

Part 2 Usage

2.1 Interfaces

The GRTK module can be used as a base station or as a mobile station. There are three interfaces in total, as shown in Figure 2.1. They are the Power port for powering the device, the com1 port(UART1) for communication between the Rover and the Base, and the com2 port for communicating with the flight controller to transmit positioning information and heading from internal compass. The com2 port includes UART2 and I2C, and UART2 for NMEA data, I2C for internal compass as default.

Figure 2.1 GRTK module interfaces diagram

In addition, there are four LED indicators on the front of the module. The three on the left display the module's operating status, which are 3D Fix positioning status, operating error, and RTK positioning status; a single indicator on the right is used to display the power supply status.

The GRTK module supports dual-antenna heading, and the antenna named ANT1 is the master antenna, the antenna named ANT2 is the slave antenna, and the single antenna needs to be connected to the master antenna.

2.2 Hardware connection

  • Base station connection

Figure 2.2 Base station connection diagram

Figure 2.3 Schematic diagram of base station tripod installation

  • Rover connection

Figure 2.4 Rover connection diagram

  • Dual-antenna rover connection

Figure 2.5 Dual antenna rover connection diagram

When the base station is not used, only the rover can be used as a conventional positioning device for positioning. The connection is shown in Figure 2.3.

The base station and the rover can be used together to form an RTK centimeter-level positioning system, and the base station supports plug and play.

The dual-antenna direction finding of the rover needs to keep the master-slave antenna consistent with the heading in accordance with the master-back-and-forward. The distance between the master-slave antennas should be greater than 30cm to ensure the direction finding accuracy.

  • Compass inside connection

GRTK has a compass inside that can provide extra heading data from the I2C port. Usually, autopilot has an I2C port to read the data.

The head of the compass is as Figure 2.6 shown, and should be consistent with the head of autopilot.

Figure 2.6 The head of the internal compass

2.3 Indicator light & Positioning status

There are 4 indicators on the GRTK module, the specific meanings are shown in the table below:

Light Status Describe
FIX On Enter 3D Fixed state.
Off Not in 3D Fixed state.
ERR On Error! The module does not work properly.
Off No error has occurred and is working properly.
RTK On Enter RTK Fixed state.
Off Not in RTK Fixed state.
PWR On The power supply is OK.
Off The power supply is abnormal.
  • When the Base is working properly, the status light changes：

PWR and FIX are on，the other lights are off.

  • When the Rover is working properly, there are two conditions in which the status light changes:

    PWR and FIX are on，the other lights are off, that means Rover has been in 3D Fixed state.
    PWR, FIX and RTK are on, the other lights are off, that means Rover has been in RTK Fixed state.

2.4 Positioning data description

The GRTK module outputs NMEA protocol positioning data by default, connects computer with GRTK module’s Tx2 and Rx2 by USB-to-TTL module, then you can use the serial assistant to read or configure the output message.

GRTK Rover and Base are factory configured, non-professionals do not configure equipment please. PS: Please set the line break to CR&LF.

2.4.1 Rover with a single antenna

$GPGGA: Global positioning system fix data
$GPRMC: Recommended minimum data
$GPHDT: Output current heading information
$KSXT: Time, positioning and heading of GNSS receiver

  • Other messages

    If needed, you can send ASCII syntax by serial port to configurate it：

Configuration Format: GPXXX COMX XX（message + output port + output rate） SAVECONFIG（Save configuration）

  • Reset

    If output message is inconsistent with the factory during use, the output can be reset by following commands:

FRESET
GPGGA COM2 0.2  
GPRMC COM2 0.2  
GPHDT COM2 0.2  
KSXT COM2 0.2
SAVECONFIG
(CR&LF)

2.4.2 Rover with dual antennas for heading

  • Output messages at 5Hz by factory default:

$GPGGA: Global positioning system fix data
$GPRMC: Recommended minimum data
$GPHDT: Output current heading information
$KSXT: Time, positioning and heading of GNSS receiver

  • Other messages

    If needed, you can send ASCII syntax by serial port to configurate it：

FRESET
GPGGA COM2 0.2  
GPRMC COM2 0.2  
GPHDT COM2 0.2  
KSXT COM2 0.2
SAVECONFIG
(CR&LF)

Configuration Format: GPXXX COMX XX（message + output port + output rate） SAVECONFIG（Save configuration）

  • Reset

    If output message is inconsistent with the factory during use, the output can be reset by following commands:

Part 3 Guidance for Use

The current version of the GRTK cm positioning system supports the output of NMEA protocol positioning data, the following guidance is based on the Ardupilot firmware(v4.2.0 or higher) using the Mission Planer ground station.

3.1 Connection for modules

  • Have the hardware, including Pixhawk controller, GRTK, radio, battery, etc, shown in Figure 3.1 ready for connection before wiring:

Figure 3.1 Hardware physical diagram

  • Rover Base and data transmissions need to be supplied separately.

3.2 The communication mode between Rover and Base

GRTK can achieve RTK positioning by communicating through independent links between the base station and the rover station or by forwarding the base station data by the ground station.

  • Independent link
    a.Please connect the COM2 port(TX2 RX2) of the GRTK Rover to the GPS port of Pixhawk and the com1 port(TX1 RX1) to connect the data transmission device that communicates with the Base side.
    b.Connect antenna to the GRTK Base and connect the com1 port of the base side to the data transmission device that communicates with the Rover terminal.
  • Forwarding the base station data by the ground station
    a.Please connect the COM2 port(TX2 RX2) of the GRTK Rover to the GPS port of Pixhawk.
    b.Connect the GRTK Base com1 port(TX1 RX1) to the computer through the serial port.
    c.Open Mission Planner, find the Optional Hardware at the Initial Setup, and select RTK/GPS Inject.

d.Choose the correct com port and click Connect.

e.Wait for about one minute for Base to complete the base station positioning, at this time the red in the RTCM column turns green, and the latitude and longitude information of the current base station is displayed, that is, the ground station has been realized to forward the Base positioning data

3.3 Mission Planner settings

3.3.1 RTK settings

GRTK Base supports plug-and-play and does not require additional setup at the ground station. However, before actually using RTK, you need to set the parameters for flight control in MP, and the necessary parameter settings are given below, which can be referred to as follows:

https://ardupilot.org/copter/docs/common-gps-for-yaw.html
  • Configure the GPS protocol as NMEA and set the GPS data refresh rate to 5Hz.
  • GPS_TYPE is set to 5 to configure the GPS protocol as NMEA.
  • GPS_RATE_MS is set to 200ms, meaning the GPS data refresh rate is 5Hz.
  • Set GRTK as the source of yaw
  • EK3_SRC1_YAW is set to 2 to set GPS as the source of yaw.
  • COMPASS_ENABLE is set to 0 to disable compass if needed.

3.3.2 Compass inside settings

a. If you connect GRTK to autopilot by I2C correctly, you can see an extra compass when you connect the autopilot to MP.

b. Set the compass as External.

c. If you want to use the compass only, you need to disable the other compasses and enable the compass of GRTK.

3.4 Positioning testing

  • Quickly deployed within 30s.

  • Unmanned vehicle automatic route mission measurement.

Part 4 Modes of Base Station

GRTK Base has two modes of operation，self-optimizing base station and fixed base station.

  • Self-optimizing base station：When it is not clear exactly where the base station will be located, Base will position itself and average itself for a certain period of time after installation as the coordinates of the base station.
  • Fixed base station: When know the exact coordinates of the base station location will be set up, you need to enter that exact coordinate into the base station.

4.1 Self-optimizing base station

  • Base station default operating mode is self-optimizing base station. Using USB to TTL module to connect the base station serial 2 (Rx2&Tx2) to the computer, the computer runs serial debugging assistant, open the corresponding serial port with the baud rate of 115200. The base station returns the current location information.

  • Send the following command (PS: Commands need to end with a line break) to base station by serial to complete configuration.

  • mode base time 60 1.5 2.5

    Within 60-second automatic positioning of the base station, or when the standard deviation of horizontal positioning is no more than 1.5 m and that of vertical positioning is no more than 2.5 m, set the average value of horizontal and vertical positioning results as the base station coordinates. Restarting the base station triggers a new calculation and reposition of the datum coordinates. Users can modify parameters according to their needs.

  • After configuration, send the following command (PS: Commands need to end with a line break) to base station by serial to save configuration.

  • saveconfig

4.2 Fixed base station

Fixed base station mode configuration is divided into two steps, the first step is to obtain the current exact coordinates, the second step is to enter the base station's precise coordinates into the base station.

Step1: Get the current exact coordinates

Using the USB-to-TTL module to connect the base station serial 2 to the computer, the computer runs the serial debugging assistant, open the corresponding serial port, Baud rate of 115200. The base station returns the current location information.

  • Send the following command (PS: Commands need to end with a line break) to base station by serial to complete configuration.

  • mode base time 60 1.5 2.5

    Within 60-second automatic positioning of the base station, or when the standard deviation of horizontal positioning is no more than 1.5 m and that of vertical positioning is no more than 2.5 m, set the average value of horizontal and vertical positioning results as the base station coordinates. Restarting the base station triggers a new calculation and reposition of the datum coordinates. Users can modify parameters according to their needs.

  • Note that the obtained WGS84 coordinates indicate that the base station initialization is complete when the data is stable.

Step2: Enter the exact coordinates of the base station into the base station

  • Copy the location information of the base station output

Example: 

#BESTPOSA,COM2,0,91.0,FINE,2164,52077.000,420887,32,18;SOL_COMPUTED,FIXEDPOS,32.02245993006,118.85899391094,68.5505,2.0115,WGS84,0.0000,0.0000,0.0000,"",0.000,0.000,40,28,28,16,0,06,03,53\*17b29c25

  • Analyze and get longitude, latitude and elevation data

Please replace it with the actual measurement data 

32.02245993006,118.85899391094,68.5505

  • The configuration command is generated based on the exact coordinates of the base station
mode base 32.02245993006 118.85899391094 68.5505

Send the configuration command (note that the command needs to end with a line break) to the base station through a serial port.

  • When the configuration is complete, the following command (note that they need to end with a line break) is sent to the base station through a serial port to save the configuration.

html saveconfig -

Part 5 Precautions

  • With our GRTK Kit, the base station side supports plug-and-play. If only Rover is purchased, the use of other companies' base station end requires additional RTK base station configuration at the ground station, which does not guarantee compatibility and positioning accuracy.
  • This product is positioning equipment, which needs to search for satellite positioning, try to test it in the open and undisturbed site.
  • The positioning status of GRTK should be mainly decided by the ground station.

Part 6 Purchase

AliExpress: GRTK (BLI Store)

6.2 List

6.3 Express delivery

Appropriate logistics methods need to be adopted according to the actual situation.

6.4 Wholesale

Wholesale prices vary depending on the quantity of the wholesale, please email us(blicube.sp@gmail.com) for more details.