Configure NTRIP-Based RTK GPS with I2C Connection

A global positioning system (GPS) receives signals from satellites in the earth’s orbit to determine where it is and how fast it is going. All supported GPS models provide data for the Position, CompassHeading, LinearVelocity, and GetAccuracy methods. You can obtain fix and correction data by using the sensor GetReadings method, which is available because GPSes wrap the sensor component.

The gps-nmea-rtk-pmtk and gps-nmea-rtk-serial movement sensor models support NTRIP-based real time kinematic positioning (RTK) GPS units (such as these) and RTCM versions up to 3.3.

The chip requires a correction source to get to the required positional accuracy. The gps-nmea-rtk-pmtk model uses an over-the-internet correction source like an RTK reference station and sends the data over I²C to the board.

Follow the guide to Set up a SparkFun RTK Reference Station to configure a SparkFun station for use with this RTK-enabled GPS movement sensor model.

• Config Builder
• JSON Template
• JSON Example

Navigate to the CONFIGURE tab of your machine’s page in the Viam app. Click the + icon next to your machine part in the left-hand menu and select Component. Select the movement-sensor type, then select the gps-nmea-rtk-pmtk model. Enter a name or use the suggested name for your movement sensor and click Create.

Fill in the attributes as applicable to your movement sensor, according to the table below.

{
  "components": [
    {
      "name": "<your-sensor-name>",
      "model": "gps-nmea-rtk-pmtk",
      "type": "movement_sensor",
      "namespace": "rdk",
      "attributes": {
        "i2c_addr": <int>,
        "i2c_baud_rate": <int>,
        "i2c_bus": "<index-of-bus-on-board>",
        "ntrip_connect_attempts": <int>,
        "ntrip_mountpoint": "<identifier>",
        "ntrip_password": "<password for NTRIP server>",
        "ntrip_url": "<URL of NTRIP server>",
        "ntrip_username": "<username for NTRIP server>"
      },
      "depends_on": [],
    }
  ]
}

{
  "components": [
    {
      "name": "my_GPS",
      "model": "gps-nmea-rtk-pmtk",
      "type": "movement_sensor",
      "namespace": "rdk",
      "attributes": {
        "i2c_addr": 66,
        "i2c_baud_rate": 115200,
        "i2c_bus": "1",
        "ntrip_connect_attempts": 12,
        "ntrip_mountpoint": "MNTPT",
        "ntrip_password": "pass",
        "ntrip_url": "http://ntrip/url",
        "ntrip_username": "usr"
      },
      "depends_on": []
    }
  ]
}

The following attributes are available for a gps-nmea-rtk-pmtk movement sensor:

Test the movement sensor

After you configure your movement sensor, open the movement sensor’s TEST panel on the CONFIGURE or CONTROL tabs. This panel presents the data collected by the movement sensor. The sections in the panel include the position, linear velocity and compass heading.

Next steps

For more configuration and development info, see: