pygnssutils

Current Status | Installation | GNSSReader | gnssdump CLI | gnssserver CLI | Troubleshooting | Graphical Client | Author & License

pygnssutils is an original Python 3 library which reads, parses and broadcasts the NMEA, UBX or RTCM3 output of any GNSS receiver, as well as providing a variety of GNSS utility classes and functions.

It consolidates the common capabilities of three existing core GNSS protocol libraries from the same stable:

1. pynmeagps (NMEA Protocol)
2. pyubx2 (UBX Protocol)
3. pyrtcm (RTCM3 Protocol)

NB: pygnssutils does not replace these libraries. pynmeagps, pyubx2 and pyrtcm will continue to be developed as independent libraries for their specific protocol parsing and generation capabilities, but functionality which is common to all three (such as reading from a GNSS data stream, and certain helper classes and functions) will be incorporated into pygnssutils. The motivation is to reduce code duplication between these libraries, reduce maintenance and testing overheads, minimise churn on the core protocol libraries, and act as a framework for future generic GNSS capabilities.

The common capabilities supported by this initial Alpha release of pygnssutils include:

1. GNSSReader class which reads and parses the NMEA, UBX or RTCM3 output of a GNSS device. This consolidates (and will in due course replace) the *Reader.read() methods in the core libraries.
2. GNSSStreamer class which forms the basis of a gnssdump CLI utility. This will in due course replace the equivalent command line utilities in the core libraries.
3. GNSSServer class which forms the basis of a gnssserver CLI utility. This implements a TCP Socket Server for GNSS data streams which is also capable of being run as a simple NTRIP Server.
4. A variety of helper classes and functions, including lat/lon coordinate conversions, socket handlers and GNSS-related mathematical functions.

The pygnssutils homepage is located at https://github.com/semuconsulting/pygnssutils.

Current Status

Sphinx API Documentation in HTML format is available at https://www.semuconsulting.com/pygnssutils.

Contributions welcome - please refer to CONTRIBUTING.MD.

Bug reports and Feature requests - please use the templates provided.

Installation

pygnssutils is compatible with Python >=3.7. See requirements for dependencies. It is recommended that the Python 3 scripts (bin) folder is in your PATH.

In the following, python3 & pip refer to the Python 3 executables. You may need to type python or pip3, depending on your particular environment.

The recommended way to install the latest version of pygnssutils is with pip:

python3 -m pip install --upgrade pygnssutils

If required, pygnssutils can also be installed into a virtual environment, e.g.:

python3 -m pip install --user --upgrade virtualenv
python3 -m virtualenv env
source env/bin/activate (or env\Scripts\activate on Windows)
(env) python3 -m pip install --upgrade pygnssutils
...
deactivate

GNSSReader

class pygnssutils.gnssreader.GNSSReader(stream, *args, **kwargs)

You can create a GNSSReader object by calling the constructor with an active stream object. The stream object can be any data stream which supports a read(n) -> bytes method (e.g. File or Serial, with or without a buffer wrapper). GNSSReader implements an internal SocketStream class to allow sockets to be read in the same way as other streams (see example below).

Individual input NMEA, UBX, or RTCM3 messages can then be read using the GNSSReader.read() function, which returns both the raw binary data (as bytes) and the parsed data (as a UBXMessage, NMEAMessage or RTCMMessage object). The function is thread-safe in so far as the incoming data stream object is thread-safe. GNSSReader also implements an iterator.

The constructor accepts the following optional keyword arguments:

• protfilter: 1 = NMEA, 2 = UBX, 4 = RTCM3 (can be OR'd. default is 7 - NMEA & UBX & RTCM3)
• quitonerror: 0 = ignore errors, 1 = log errors and continue (default), 2 = (re)raise errors and terminate
• validate: VALCKSUM (0x01) = validate checksum (default), VALNONE (0x00) = ignore invalid checksum or length
• parsebitfield: 1 = parse bitfields (UBX 'X' type properties) as individual bit flags, where defined (default), 0 = leave bitfields as byte sequences
• msgmode: 0 = GET (default), 1 = SET, 2 = POLL

Usage:

Example - Serial input. This example will output both UBX and NMEA messages:

>>> from serial import Serial
>>> from pygnssutils import GNSSReader
>>> stream = Serial('/dev/tty.usbmodem14101', 9600, timeout=3)
>>> gnr = GNSSReader(stream)
>>> (raw_data, parsed_data) = gnr.read()
>>> print(parsed_data)

Example - File input (using iterator). This will only output UBX data:

>>> from pygnssutils import GNSSReader
>>> stream = open('ubxdata.bin', 'rb')
>>> gnr = GNSSReader(stream, protfilter=2)
>>> for (raw_data, parsed_data) in gnr: print(parsed_data)
...

Example - Socket input (using enhanced iterator). This will output UBX, NMEA and RTCM3 data:

>>> import socket
>>> from pygnssutils import GNSSReader
>>> stream = socket.socket(socket.AF_INET, socket.SOCK_STREAM):
>>> stream.connect(("localhost", 50007))
>>> gnr = GNSSReader(stream, protfilter=7)
>>> for (raw_data, parsed_data) in gnr.iterate(): print(parsed_data)
...

Refer to the Sphinx API documentation for further details.

GNSSStreamer and gnssdump CLI

class pygnssutils.gnssdump.GNSSStreamer(**kwargs)

GNSSStreamer is essentially a CLI wrapper around the GNSSReader class. It supports a variety of input streams (including serial, file and socket) and outputs either to stdout (terminal) or to custom protocol handlers. A custom protocol handler can be a writeable output medium (serial, file, socket or queue) or an evaluable Python expression (e.g. lambda).

The utility can output data in a variety of formats; parsed (1), raw binary (2), hexadecimal string (4), tabulated hexadecimal (8) or any combination thereof. (FYI a JSON output format is currently under development)

Any one of the following data stream specifiers must be provided:

• port: serial port e.g. COM3 or /dev/ttyACM1
• filename: fully qualified path to binary input file e.g. /logs/logfile.bin
• socket: socket e.g. 192.168.0.72:50007 (port must be specified)
• stream: any other instance of a stream class which implements a read(n) -> bytes method

For help and full list of optional arguments, type:

> gnssdump -h

Refer to the Sphinx API documentation for further details.

Usage:

Assuming the Python 3 scripts (bin) directory is in your PATH, the CLI utility may be invoked from the shell thus:

Serial input example (with simple external UBX protocol handler):

> gnssdump port=/dev/ttyACM1 baud=9600 timeout=5 quitonerror=1 protfilter=2 msgfilter=NAV-PVT ubxhandler="lambda msg: print(f'lat: {msg.lat}, lon: {msg.lon}')"

Parsing GNSS data stream from serial: Serial<id=0x10fe8f100, open=True>(port='/dev/ttyACM1', baudrate=9600, bytesize=8, parity='N', stopbits=1, timeout=5, xonxoff=False, rtscts=False, dsrdtr=False)...

lat: 51.352179, lon: -2.130762
lat: 51.352155, lon: -2.130751

File input example (in tabulated hexadecimal format):

> gnssdump filename=pygpsdata.log quitonerror=2 format=8 protfilter=1 msgfilter=GPGGA,GPGSA

Parsing GNSS data stream from file: <_io.BufferedReader name='pygpsdata.log'>...

000: 2447 5047 4741 2c30 3830 3234 372e 3030  | b'$GPGGA,080247.00' |
016: 2c35 3332 372e 3034 3330 302c 4e2c 3030  | b',5327.04300,N,00' |
032: 3231 342e 3431 3338 352c 572c 312c 3037  | b'214.41385,W,1,07' |
048: 2c31 2e36 332c 3336 2e37 2c4d 2c34 382e  | b',1.63,36.7,M,48.' |
064: 352c 4d2c 2c2a 3737 0d0a                 | b'5,M,,*77\r\n' |

000: 2447 5047 5341 2c41 2c33 2c30 322c 3133  | b'$GPGSA,A,3,02,13' |
016: 2c32 302c 3037 2c30 352c 3330 2c30 392c  | b',20,07,05,30,09,' |
032: 2c2c 2c2c 2c32 2e34 342c 312e 3633 2c31  | b',,,,,2.44,1.63,1' |
048: 2e38 322a 3035 0d0a                      | b'.82*05\r\n' |

GNSSSocketServer and gnssserver CLI

class pygnssutils.gnssserver.GNSSSocketServer(**kwargs)

This is essentially a CLI wrapper around the GNSSStreamer and SocketServer classes (the latter based on the native Python ThreadingTCPServer framework) which uses queues to transport data between the two classes.

Usage:

Assuming the Python 3 scripts (bin) directory is in your PATH, the CLI utility may be invoked from the shell thus:

> gnssserver inport="/dev/tty.usbmodem14101" hostip=192.168.0.20 outport=6000

Any arguments not provided will be defaulted;

• default hostip = 0.0.0.0 (i.e. binds to all available host IP address)
• default inport = "/dev/ttyACM1"
• default outport = 50010

In its default configuration (ntripmode=0) it acts as an open, unauthenticated TCP socket server, reading the binary data stream from a host-connected GNSS receiver and broadcasting the data to any TCP socket client running on a local or remote machine (firewalls permitting). Suitable clients include (but are not limited to):

1. pygnssutils's gnssdump cli utility invoked thus:

> gnssdump socket=hostip:outport

2. The PyGPSClient GUI application.

It can be run as a daemon process (or even a service) but note that abrupt termination (i.e. without invoking the internal server.shutdown() method) may result in the designated TCP socket port being unavailable for a short period - this is operating system dependant. It also supports most of the gnssdump keyword arguments and could be configured to output a variety of non-binary formats, but the user would need to construct appropriate bespoke socket clients to parse such data formats.

NTRIP Mode:

'gnssserver' can also be configured to act as a single-mountpoint NTRIP Server, broadcasting RTCM3 RTK correction data to any authenticated NTRIP client on the standard 2101 port:

> gnssserver inport="/dev/tty.usbmodem14101" hostip=192.168.0.20 outport=2101 ntripmode=1 protfilter=4

NOTE THAT this configuration is predicated on the host-connected receiver being an RTK-capable device (e.g. the u-blox ZED-F9P) operating in 'Base Station' mode (either 'SURVEY_IN' or 'FIXED') and outputting the requisite RTCM3 RTK correction messages (1005, 1077, 1087, 1097, 1127, 1230). NTRIP server login credentials are set via environment variables PYGPSCLIENT_USER and PYGPSCLIENT_PASSWORD. Suitable clients include, but are not limited to, PyGPSClient's NTRIP Client facility - PyGPSClient can also be used to configure the host receiver.

For help and full list of optional arguments, type:

> gnssserver -h

Refer to the Sphinx API documentation for further details.

Troubleshooting

1. Unknown Protocol errors.

These are usually due to corruption of the serial data stream, either because the serial port configuration is incorrect (baud rate, parity, etc.) or because another process is attempting to use the same data stream.

• Check that your UBX receiver UART1 or UART2 ports are configured for the desired baud rate - remember the factory default is 38400 (not 9600).
• Check that no other process is attempting to use the same serial port, including daemon processes like gpsd.

2. Serial Permission errors.

These are usually caused by inadequate user privileges or contention with another process.

• On Linux platforms, check that the user is a member of the tty and/or dialout groups.
• Check that no other process is attempting to use the same serial port, including daemon processes like gpsd.

3. UnicodeDecode errors.

• If reading UBX data from a log file, check that the file.open() procedure is using the rb (read binary) setting e.g. stream = open('ubxdatalog.log', 'rb').

4. Reading from NMEA log file returns no results.

• If reading from a binary log file containing NMEA messages, ensure that the message terminator is CRLF (\r\n or x0d0a) rather than just LF (\n or 0x0a). Some standard text editors may replace a CRLF with LF - use a dedicated hex editor instead.

Graphical Client

A python/tkinter graphical GPS client which supports NMEA, UBX and RTCM3 protocols is available at:

https://github.com/semuconsulting/PyGPSClient

Author & License Information

semuadmin@semuconsulting.com

pygnssutils is maintained entirely by unpaid volunteers. If you find it useful, a small donation would be greatly appreciated!