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read

Read data from GPS receiver

Description

example

[tt,overrun] = read(gps) returns the GPS readings in timetable format. This is a non blocking read which returns N data points in timetable format, where N is specified by SamplesPerRead property and timetable is specified using OutputFormat property of gpsdev object.

example

[lla,groundSpeed,course,dops,gpsReceiverTime,timestamp,overrun] = read(gps) returns matrices of measurements from the GPS. This is a non blocking read which returns N data points in matrix format, where N is specified by SamplesPerRead property and matrix is specified using OutputFormat property of the gpsdev object.

Examples

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Read data from the GPS receiver connected to the host computer on a specific serial port.

Required Hardware

To run this example, you need:

  • UBlox Neo-6M GPS module

  • GPS antenna

  • USB to UART module

  • USB cable

  • Connecting wires

Hardware Connection

Connect the pins on the UBlox Neo-6M GPS module to the pins on your USB to UART module. The connections are:

  • VCC - +5V

  • RX - TXO

  • TX - RXI

  • GND - GND

Connect the GPS antenna to the GPS module. Connect the USB to UART module to the host computer with a USB cable. GPS Fix can be easily acquired in locations that have a clear view of the sky. Wait for the GPS module to acquire satelite signals (Fix).This can be verified by checking the Fix LED (D1) of your GPS module.

Create GPS Object

Create a gpsdev object for the GPS receiver connected to a specific port. Specify the output format of the data as a timetable.

gps = gpsdev('COM4','OutputFormat',"timetable")
gps = 
  gpsdev with properties:

                         SerialPort: COM4	
                           BaudRate: 9600 (bits/s)

                     SamplesPerRead: 1	 
                           ReadMode: "latest"	 
                        SamplesRead: 0	 
Show all properties all functions

Read the GPS data

Read the GPS data and return them as a timetable.

[tt,overruns] = read(gps)
tt=1×5 timetable
              Time                         LLA               GroundSpeed    Course            DOPs                GPSReceiverTime     
    ________________________    _________________________    ___________    ______    ____________________    ________________________

    22-Mar-2021 15:31:15.190    17.47    78.343     449.6      0.25619       NaN      9.31    1.48    9.19    22-Mar-2021 10:01:14.000

overruns = 0

Display number of samples read and the samples available in the host buffer.

gps.SamplesRead
ans = 1
gps.SamplesAvailable
ans = 0

Release the GPS object to configure the non tunable properties. The release function also clears the buffer and resets the SamplesRead and SamplesAvailable properties.

release(gps)

Specify the number of samples per read to 2. Read the GPS data.

gps.SamplesPerRead = 2;
read(gps)
ans=2×5 timetable
              Time                         LLA               GroundSpeed    Course            DOPs                GPSReceiverTime     
    ________________________    _________________________    ___________    ______    ____________________    ________________________

    22-Mar-2021 15:31:17.178    17.47    78.343       450     0.063791       NaN      9.32    1.48     9.2    22-Mar-2021 10:01:16.000
    22-Mar-2021 15:31:17.178    17.47    78.343       450     0.063791       NaN      9.32    1.48     9.2    22-Mar-2021 10:01:16.000

Display number of samples read and the samples available in the host buffer.

gps.SamplesRead
ans = 1
gps.SamplesAvailable
ans = 0

Clean Up

When the connection is no longer needed, clear the associated object.

delete(gps);
clear gps;

Read data from the GPS receiver connected to the host computer using serialport object.

Required Hardware

To run this example, you need:

  • UBlox Neo-6M GPS module

  • GPS antenna

  • USB to UART module

  • USB cable

  • Connecting wires

Hardware Connection

Connect the pins on the UBlox Neo-6M GPS module to the pins on your USB to UART module. The connections are:

  • VCC - +5V

  • RX - TXO

  • TX - RXI

  • GND - GND

Connect the GPS antenna to the GPS module. Connect the USB to UART module to the host computer with a USB cable. GPS Fix can be easily acquired in locations that have a clear view of the sky. Wait for the GPS module to acquire satelite signals (Fix).This can be verified by checking the Fix LED (D1) of your GPS module.

Create GPS Object

Connect to the GPS receiver using serialport object. Specify the port name and the baud rate. Specify the output format of the data as matrix.

s = serialport('COM4',9600);
gps = gpsdev(s,'OutputFormat',"matrix")
gps = 
  gpsdev with properties:

                         SerialPort: COM4	
                           BaudRate: 9600 (bits/s)

                     SamplesPerRead: 1	 
                           ReadMode: "latest"	 
                        SamplesRead: 0	 
Show all properties all functions

Read the GPS data

Read the GPS data and return them as matrices.

[lla,speed,course,dops,gpsReceiverTime,timestamp,overruns] = read(gps)
lla = 1×3

   NaN   NaN   NaN

speed = NaN
course = NaN
dops = 1×3

   NaN   NaN   NaN

gpsReceiverTime = datetime
   NaT

timestamp = datetime
   22-Mar-2021 03:41:00.274

overruns = 1

Display number of samples read and the samples available in the host buffer.

gps.SamplesRead
ans = 1
gps.SamplesAvailable
ans = 0

Flush all GPS data accumulated in the buffers and reset the SamplesRead and SamplesAvailable properties.

flush(gps)

Display number of samples read and the samples available in the host buffer.

gps.SamplesRead
ans = 0
gps.SamplesAvailable
ans = 0

Clean Up

When the connection is no longer needed, clear the associated object.

delete(gps);
clear gps;
clear s;

Input Arguments

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The GPS sensor, specified as a gpsdev object.

Output Arguments

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GPS data, returned as a timetable. The timetable returned has the following fields:

  • LLA (Latitude, Longitude, Altitude)

  • Ground Speed

  • Course over ground

  • Dilution of Precisions(DOPs), VDOP,HDOP,PDOP

  • GPS Receiver Time

  • Time — System time when the data is read, in datetime or duration format

Data Types: timetable

Position of the GPS receiver in the geodetic latitude, longitude, and altitude (LLA), returned as a real finite N-by-3 array. Latitude and longitude are in degrees with North and East being positive. Altitude is in meters.

Data Types: double

Speed over ground, returned as a real finite N-by-1 vector.

Data Types: double

Course over ground relative to true north, returned as a real finite N-by-1 vector of values between 0 and 2pi radians.

Data Types: double

Dilution of precisions, returned as a real finite N-by-3 matrix of the form [PDOP,HDOP,VDOP].

Data Types: double

UTC time, returned as a N-by-1 vector.

Data Types: datetime

Time at which GPS data is read, returned as a real finite N-by-1 vector. This is the system time. If the TimeFormat is datetime, the timestamp will be datetime. If the TimeFormat is a duration, the timestamp will be duration

  • datetime — Displays the date and time at which the data is read.

  • duration — Displays the time elapsed in seconds after the first call of the read function or the last execution of the release function.

Note

If the SamplesPerRead is greater than 1, an extrapolation is done on the time value. Hence it might not be precise.

Data Types: datetime | duration

The number of samples lost between consecutive calls to read. The overrun is zero when ReadMode is set to oldest.

Data Types: double

More About

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read Output

The gpsdev object expects GPRMC, GPGGA, and GPGSA sentences as outputs from the GPS receiver to get the required values. The read function errors out if these sentences are not available.

The read function outputs NaN and NaT in the following situations:

  • If the GPS module does not receive valid data because there is no satellite lock or when GPS does not give a particular value.

  • If there is a checksum failure, corresponding data points will be NaN for numeric outputs (lla, speed, course, dops) and NaT for gpsRecieverTime. lla is taken from GPGGA sentence, speed,course, and gpsRecieverTime is taken GPRMC sentence and dops are taken from GPGSA sentence.

Because read function is non blocking, the following is expected:

  • If no new data is available, the output of read is the previous data. For example, if the delay between subsequent reads is less than the UpdateRate of the GPS receiver.

Because GPS data is validated in the first read operation, it might take more time compared to the subsequent read operations.

See Also

Objects

Functions

Introduced in R2020b