MAX-M8Q GNSS HAT
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Instruction
Positioning Principle
What's GNSS
GNSS (Global Navigation Satellite System) is a general term for multiple satellite systems. At present, there are BDS (China), GLONASS (Russia), GPS (United States), Galileo (Europe), QZSS (Japan), IRNSS (India) navigation satellite systems in the world. The features of GNSS are as follows:
- GPS is widely used with mature technology, and the frequency band signals such as L1C/A, L2C, L5, have improve the positioning accuracy.
- GNSS module with multi-system and multi-band can capture satellites from different satellite systems, which greatly increases the number of effective satellites and improves positioning accuracy and stability.
- The signal received by the GNSS module contains reflected and refracted signals, resulting in multi-path effects that affect the positioning accuracy. The multi-band and multi-constellation system technology can effectively lessen errors caused by the atmosphere and improve positioning accuracy.
- With the development of GNSS, a variety of positioning technologies such as RTK, PPP-RTK and multi-sensor fusion positioning DR (Dead Reckoning) have emerged to meet the needs of differentiated high-precision positioning.
GPS Principle
In this section, the working principle of GPS receiver positioning is shown in the figure below, and the details are described in the following 5 points. For details of the positioning principle, please refer to GPS Working Principle, Fundamentals of gps receivers, FUNDAMENTALS OF GPS
- GPS satellites continuously send radio signals with their own time and position information in the air for GPS receivers (GNSS modules such as ZED-F9P)
- A pseudo-random code will be generated inside the satellite and the receiver. Once the two pseudo-random codes are synchronized, the receiver can measure the difference between the time the radio signal is transmitted and the time it arrives at the receiver (referred to as the time delay), and multiply the time delay by the speed of light to get the distance (pseudorange)
- The time of GPS system is maintained by the rubidium atomic frequency standard of the atomic clocks on each satellite. These satellite clocks are generally accurate to within a few nanoseconds of Coordinated Universal Time (UTC), which is maintained by the Naval Observatory's "Master Clock" , the stability of each master clock is several 10^(-13) seconds.
- Computers and navigation information generators on GPS satellites know precisely their orbital positions and system time, while a global network of monitoring stations keeps track of satellites' orbital positions and system time. The main control station at Schriever Air Force Base in Colorado, together with its operation and control section, input the orbital position and on-board clock correction data calculated on the basis of complex models into each GPS satellite at least once a day.
- To calculate the 3D position of the GPS receiver (GNSS module), the GPS receiver is required to receive signals from at least four satellites, and the 3D position is calculated according to the space triangle Pythagorean theorem and the quadratic linear equation.
What's RTK
RTK (Real Time Kinematic), also known as carrier phase differential technology, is a GNSS positioning technology that supports centimeter-level positioning accuracy (referred to as RTK), and is a differential method for real-time processing of the carrier phase observations of two measuring stations. The working process of RTK is shown in the figure below. The DGPS corrections generated by the base station (GNSS receiver) are transmitted to the mobile station (GNSS receiver) in real time through the mobile network for calculation and centimeter positioning.
RTK Application
- Apply in various control surveys such as traditional geodetic surveying and engineering control surveying in triangulation and wire netting methods, and use RTK to measure the positioning accuracy in real time to ensure observation quality and improve operational efficiency. Compared with non-real-time measurement such as normal GPS static surveys, fast static survey, pseudo-dynamic survey, it must be retested when the accuracy does not meet the requirements.In addition, RTK is used in highway control measurement, electronic circuit control measurement, water conservancy engineering control measurement, geodetic survey, which can reduce labor intensity and save costs, and can complete control point measurement within minutes or even seconds.
- Topographic mapping: Using RTK only requires one person with the instrument to stay at the detail point for a second or two, and input the feature code at the same time. The accuracy of point and area can be known in real time through the screen. After returning to the room, the professional software interface can output the required topographic map. In this way, RTK only requires one person to operate, and it does not require point-to-point vision, which greatly improves efficiency. With RTK and electronic handbook, you can measure and design various topographic maps, such as general surveying, railway strip topographic map, highway pipeline topographical map, can measure reservoir topographic map, nautical ocean surveying and so on with the depth sounder.
- Setting out is an application branch of measurement. When using RTK to set out, you only need to input the designed point coordinates into the electronic handbook with the GPS receiver on your back, and it will remind you to go to the position. It is not only fast and easy, but also is high-accuracy and uniform as GPS is set out by coordinates directly. Hence, the efficiency of setting out in exterior operation is greatly improved, and only one person can operate.
Test it in Windows PC
1. Download and install u-center software and then open it
2. Set the jumpers on A area, assemble GNSS antenna,and set the receiver of antenna on open area outside. Connect the micro USB interface to PC
3. Note that you should set the side without sticker upward, Open Device Manager and check the COM port, connect MAX-M8Q, and use auto-baudrate
4. Power the MAX-M8Q module and set it to 3D mode, select File ->Database Export ->Google Map Html to export file
5. Download Test file, upzip and open it by Chrome browser, import the file which is saved from u-center above to check position information.
6. Please refer to the User guide about how to use the u-center.
Using with Raspberry Pi
Hardware Connection
| PIN | Raspberry Pi(BCM) | Raspberry Pi(WiringPi) | Descruption |
| 5V | - | - | 5V Power input |
| GND | - | - | Ground |
| RXD | P14 | P15 | Receiver pin of UART |
| TXD | P15 | P16 | Transmit pin of UART |
| SDA | P2 | P8 | SDA pin of I2C |
| SCL | P3 | P9 | SCL pin of I2C |
| PPS | P18 | P1 | PPS pin of module |
| INT | P27 | P2 | Wakeup pin, low active |
Enable Serial Port
Open the Raspberry Pi Terminal and configure by commands
sudo raspi-config #Choose Interfacing Options -> Serial -> No -> Yes #You should disable shell login and enable the hardware serial sudo reboot
Install and Modify Parameters
- Install Python library function
sudo apt-get update sudo apt-get install gpsd gpsd-clients gpsd-tools sudo pip3 install gps3
- Modify gpsd
#Open gpsd file sudo nano /etc/default/gpsd #Change the below codes of file and save USBAUTO="false" DEVICES="/dev/ttyS0" GPSD_OPTIONS="/dev/ttyUSB0"
- Download demo codes
mkdir ~/Documents/MAX-XXX_GNSS_HAT_Code cd ~/Documents/MAX-XXX_GNSS_HAT_Code/ wget https://www.waveshare.com/w/upload/0/0f/MAX-XXX_GNSS_HAT_Code.zip unzip MAX-XXX_GNSS_HAT_Code.zip
Python Example
Enter the python directory (demo codes), and run the example.
cd ~/Documents/MAX-XXX_GNSS_HAT_Code/RaspberryPi/python/coordinate_converter sudo python3 main.py
NTP Server
The system clock of personal computers, servers and other equipment will be skewed as shown in the figure below. High-precision clock scenarios will be affected in high-frequency trading systems, automated production lines, etc., while NEO-M8T can achieve coverage in harsh signal environments. It relies on the atomic clock on the satellite to ensure that the accuracy of the clock is not affected by factors such as the network. In this section, NEO-M8T and Raspberry Pi are used to build an NTP server to provide timing functions for devices in the local area network in an indoor closed environment.
1. Connect the NEO-M8T GNSS TIMING HAT to the antenna, and place the other end of the antenna near the outer wall or window sill.
2. Connect the NEO-M8T connected to the antenna to the Raspberry Pi, power it on, and wait for the NE0-M8T to output the PPS signal.
3. Copy and paste the following command to the Raspberry Pi command line to execute.
sudo apt-get install git cd ~/Documents sudo git clone https://github.com/beta-tester/RPi-GPS-PPS-StratumOne.git cd RPi-GPS-PPS-StratumOne sudo chmod 777 install-gps-pps.sh
4. The installation takes a long time, reboot the Raspberry Pi after installation
5. Open the /boot/config.txt file, jump to the last line, change gpiopin=4 to gpiopin=18, press Ctrl+X then Y and press Enter to save
sudo nano /boot/config.txt dtoverlay=pps-gpio,gpiopin=18,capture_clear # /dev/pps0
6.Use the following command to test the operation of pps0, the Raspberry Pi time has already used the time system provided by NEO-M8T
watch -n1 chronyc syntaxhighlightstats -v
7.To provide time for other devices, obtain the address of the Raspberry Pi running NTP, such as 192.168.6.93
8.For Linux devices, use the following command to synchronize the time
sudo apt install ntpdate sudo ntpdate 192.168.6.93
Using STM32 Board
Hardware Connection
| GNSS Module | XNUCLEO-F103RB | Description |
| 5V | - | 5V Power input |
| GND | GND | Ground |
| RXD | P9(TX) | Receive pin of UART |
| TXD | P10(RX) | Transmit pin of UART |
Run the example
Download the demo codes. Open the STM32 project by Keil software, compile and download it to the XNUCLEO-F103RB board, connect UART2 pins to PC and check the information by COM assistance software.
Using with Jetson Nano
- Install Python library function
sudo apt-get update sudo apt-get install python-serial sudo apt-get install gpsd gpsd-clients python-gps sudo pip3 install gps3
- Modify gpsd parameters
#Open gpsd document sudo nano /etc/default/gpsd #Modify the following parameters in the document and save the Settings to exit USBAUTO="false" DEVICES="/dev/ttyTHS1" GPSD_OPTIONS="/dev/ttyUSB0"
- Download the demo
mkdir -p ~/Documents/MAX-XXX_GNSS_HAT_Code cd ~/Documents/MAX-XXX_GNSS_HAT_Code/ wget https://www.waveshare.com/w/upload/0/0f/MAX-XXX_GNSS_HAT_Code.zip unzip MAX-XXX_GNSS_HAT_Code.zip
- Check the port for data
sudo chmod 777 /dev/ttyTHS1 sudo minicom -D /dev/ttyTHS1 -b 9600 sudo cat /dev/ttyTHS1 sudo gpsd /dev/ttyTHS1 -F /var/run/gpsd.sock sudo cgps -s sudo killall gpsd sudo reboot
python
Enter the python directory and run the demo, and you can view the information directly on Google Maps
cd ~/Documents/MAX-XXX_GNSS_HAT_Code/RaspberryPi/python/coordinate_converter sudo python3 main.py
