Configure an NTRIP-Based RTK GPS with an 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).

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 and sends the data over I2C to the board.

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.

Creation of a `gps-nmea-rtk-pmtk` movement sensor in the Viam app config builder.

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:

NameTypeInclusionDescription
i2c_addrintRequiredThe device’s I2C address.
i2c_busstringRequiredThe index of the I2C bus of the board wired to the sensor.
i2c_baud_rateintOptionalThe rate at which data is sent from the sensor. Optional.
Default: 38400
ntrip_urlstringRequiredThe URL of the NTRIP server from which you get correction data. Connects to a base station (maintained by a third party) for RTK corrections.
ntrip_usernamestringOptionalUsername for the NTRIP server.
ntrip_passwordstringOptionalPassword for the NTRIP server.
ntrip_connect_attemptsintOptionalHow many times to attempt connection before timing out.
Default: 10
ntrip_mountpointstringOptionalIf you know of an RTK mountpoint near you, write its identifier here. It will be appended to NTRIP address string (for example, “nysnet.gov/rtcm/NJMTPT1”) and that mountpoint’s data will be used for corrections.

Test the movement sensor

After you configure your movement sensor, navigate to the Control tab and select the dedicated movement sensor dropdown panel. This panel presents the data collected by the movement sensor. The sections in the panel include the position, linear velocity and compass heading.

The movement sensor component in the control tab

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