Description

The GPS Location Logger sample works with any serial port (UART) based GPS sensor or with the Xsens GPS device connected over USB. The logger requires the GPS sensor connected over serial port to deliver messages in NMEA format, while the Xsens device can run in proprietary mode.

Interfacing with sensors

Serial

Consumer grade off-the-shelf GPS sensors, also known as GPS mice (e.g., Garmin GPS), are usually connected over USB and implement a serial-to-USB connection with the help of FTDI devices. The Xsens GPS device can be connected through a serial-to-USB connection.

On Linux, these sensors can then be reached over the /dev/ttyUSB or /dev/ttyACM devices. Before trying out the sample, ensure the user has access to the serial device. You can do so by trying to read from the device e.g. with cat /dev/ttyACMx, and if permission is denied, add the current user to the dialout group and then log out/in again:

sudo usermod -a -G dialout $USER

On QNX, prior to accessing the device, launch the dev-serusb driver as follows:

devc-serusb -b <baudrate> -F -S -d path=/dev/usb/io-usb-otg

The serial devices can the be reached over the /dev/serusb devices.

Xsens USB

The Xsens GPS device can also be connected directly over USB, but is only supported on Linux.

Running the sample

The GPS Location Logger sample, sample_gps_logger, accepts the following parameters:

./sample_gps_logger --driver=[gps.virtual|gps.uart|gps.xsens|gps.novatel|gps.dataspeed|gps.custom|gps.ublox]
                    --params=[comma/separated/key/value/pairs]

Where:

--driver=[gps.virtual|gps.uart|gps.xsens|gps.novatel|gps.dataspeed|gps.custom|gps.ublox]
    Allows to specify which GPS driver to use.
    Default value: gps.virtual

--params=[comma/separated/key/value/pairs]
    Different parameters are available for each GPS driver.
    Default value: file=path/to/data/samples/sensors/gps/1.gps

Note: For a full list of key/value pairs that can be passed to –params see Sensor Enumeration Sample .

Examples

NMEA format

For serial devices transmitting messages in NMEA format, use the gps.uart driver. For example:

./sample_gps_logger --driver=gps.uart --params=device=/dev/ttyACM0

Per default, if no baud parameter has been provided the gps.uart driver assumes a baudrate of 9600. In order to change the baudrate provide baud argument as:

./sample_gps_logger --driver=gps.uart --params=device=/dev/ttyACM0,baud=115200

On QNX, the baudrate is set when starting devc-serusb. The baud parameter will be ignored.

Xsens proprietary format

The sample supports reading GPS packets from a Xsens device through the gps.xsens driver. To run the sample using Xsens over USB device use:

./sample_gps_logger --driver=gps.xsens --params=device=0,frequency=100

Where device=0 parameter sets the index of the Xsens device (usually 0 if only one device is installed) and frequency=100 sets the frequency in [Hz] this device should operate with.

To run the sample using Xsens over serial use:

./sample_gps_logger --driver=gps.xsens --params=device=/dev/ttyUSB0,frequency=100

Please note that even if the Xsens device is a shared device, like Xsens MTi-G-700, capable of delivering GPS and IMU packets, only the GPS packets will be parsed by the gps.xsens driver.

Note: If the device is connected to Xavier UART you need also specify –stop-bits=1

Sensor sharing

The sample also demonstrates how sensor sharing can be implemented. Two NVIDIA^® DriveWorks GPS sensors are created from the same hardware device. Both sensor can be then treated independently. Both sensors would deliver exactly the same set of packets. Each sensor is using, however, their own FIFO hence they can be drained at different rates. The output of both sensors is printed to the console:

GPS[0] - 2712443194 lat: 37.38652333 lon: -122.164585 alt: 46.9 course: 233.9 speed: 0 hdop: 0.8 vdop: 0.8
GPS[1] - 2712443194 lat: 37.38652333 lon: -122.164585 alt: 46.9 course: 233.9 speed: 0 hdop: 0.8 vdop: 0.8

The index [0], [1] indicates what sensor produced the output. As expected the data packets and their timestamps are equal.

Output

Any valid GPS message that is received results in an output on the console similar to:

GPS[0] - 2712443194 lat: 37.38652333 lon: -122.164585 alt: 46.9 course: 233.9 speed: 0 hdop: 0.8 vdop: 0.8

Where the first number indicates the timestamp of the received GPS message in microseconds and the rest of the line indicates the geographical location of the sensor.

If no parameters are provided, the sample starts a virtual GPS sensor and interprets the content from the file located at data/samples/sensors/gps/1.gps as GPS input.

Additional Information

For more details see GPS .

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