pyubx2 0.1.5

UBX Protocol Parser

pyubx2

pyubx2 is an original python library for the UBX protocol.

UBX is a proprietary binary protocol implemented on u-blox © GPS receiver modules.

The pyubx2 homepage is located at http://github.com/semuconsulting/pyubx2.

This is a personal project and I am in no way affiliated with u-blox.

Current Status

At time of writing the library is based on the u-blox generation 6 protocol but is readily extensible for later generations.

Implements the full range of UBX Generation 6 protocol messages with the exception of a handful of message classes which require non-standard processing (see release notes on GitHub for details). These, along with a growing subset of Generation 8 messages, are in hand.

Constructive feedback and feature requests welcome.

Compatibility

pyubx2 is compatible with Python 3.6+ and has no third-party library dependencies.

Installation

The recommended way to install pyubx2 is with pip:

pip install pyubx2

Reading (Streaming)

You can create a UBXReader 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).

Individual UBX messages can then be read using the UBXReader.read() function, which returns both the raw binary data (as bytes) and the parsed data (as a UBXMessage object). The function is thread-safe in so far as the incoming data stream object is thread-safe.

Parsing

You can parse individual UBX messages using the UBXMessage.parse(data, validate=False) function, which takes a bytes array containing a binary UBX message and returns a UBXMessage object.

If the optional 'validate' parameter is set to True, parse will validate the supplied UBX message header, payload length and checksum. If any of these are not consistent with the message content, it will raise a UBXParseError. Otherwise, the function will automatically generate the appropriate payload length and checksum.

Example:

>>> from pyubx2 import UBXMessage
>>> msg = UBXMessage.parse(b'\xb5b\x05\x01\x02\x00\x06\x01\x0f\x38', True)
>>> msg
<UBX(ACK-ACK, clsID=CFG, msgID=CFG-MSG)>
>>> msg = UBXMessage.parse(b'\xb5b\x01\x12$\x000D\n\x18\xfd\xff\xff\xff\xf1\xff\xff\xff\xfc\xff\xff\xff\x10\x00\x00\x00\x0f\x00\x00\x00\x83\xf5\x01\x00A\x00\x00\x00\xf0\xdfz\x00\xd0\xa6')
>>> msg
<UBX(NAV-VELNED, iTOW=403327000, velN=-1, velE=-21, velD=-4, speed=22, gSpeed=21, heading=128387, sAcc=67, cAcc=8056455)>

The UBXMessage object exposes different public properties depending on its message type or 'identity', e.g. the NAV-POSLLH message has the following properties:

>>> msg
<UBX(NAV-POSLLH, iTOW=403667000, lon=-21601284, lat=526206345, height=86327, hMSL=37844, hAcc=38885, vAcc=16557)>
>>>msg.identity
'NAV-POSLLH'
>>>msg.lat/10**7, msg.lon/10**7
(52.6206345, -2.1601284)
>>>msg.hMSL/10**3
37.844

Generating

You can create a UBXMessage object by calling the constructor with message class, message id, payload and mode parameters.

The 'mode' parameter is an integer flag signifying whether the message payload refers to a:

• GET message (i.e. from the receiver - the default)
• SET message (i.e. to the receiver)
• POLL message (i.e. to the receiver in anticipation of a response back)

The distinction is necessary because the UBX protocol uses the same message class and id for all three modes, but with different payloads.

e.g. to generate a outgoing CFG-MSG which polls the 'VTG' NMEA message rate on the current port:

>>> from pyubx2 import UBXMessage, POLL
>>> msg = UBXMessage(b'\x06', b'\x01', b'\xF0\x05', POLL)
>>> msg
<UBX(CFG-MSG, msgClass=NMEA-Standard, msgID=VTG)>

The constructor also supports plain text representations of the message class and id, e.g.

>>> from pyubx2 import UBXMessage, POLL
>>> msg = UBXMessage('CFG','CFG-MSG', b'\xF1\x03', POLL)
>>> msg
<UBX(CFG-MSG, msgClass=NMEA-Proprietary, msgID=UBX-03)>

Serializing

The UBXMessage class implements a serialize() method to convert a UBXMessage object to a bytes array suitable for writing to an output stream.

e.g. to create and send a CFG-MSG message which sets the NMEA GLL message rate to '1' on the receiver's UART and USB ports (assuming an output serial stream has been created as serialOut):

>>> from pyubx2 import UBXMessage, SET
>>> msg = UBXMessage('CFG','CFG-MSG', b'\xF0\x01\x00\x01\x01\x01\x00\x00', SET)
>>> msg
<UBX(CFG-MSG, msgClass=NMEA-Standard, msgID=GLL, rateDDC=0, rateUART1=1, rateUART2=1, rateUSB=1, rateSPI=0, reserved=0)>
>>> output = msg.serialize()
>>> output
b'\xb5b\x06\x01\x08\x00\xf0\x01\x00\x01\x01\x01\x00\x00\x036'
>>> serialOut.write(output)

Examples

The following examples can be found in the \examples folder:

1. ubxstreamer.py illustrates how to implement a threaded serial reader for UBX messages using pyubx2.

2. ubxconfig.py illustrates how to implement a simple configuration utility which sets output UBX-NAV message rates on the receiver's UART and USB ports (on a non-permanent basis). You can see the results using ubxstreamer.py.

3. ubxprotocol.py illustrates how to set the outbound protocols on the receiver's USB port to NMEA, UBX or both (on a non-permanent basis). You can see the results using ubxstreamer.py.

Extensibility

The UBX protocol is principally defined in the modules ubxtypes_*.py as a series of dictionaries. Additional message types can be readily added to the appropriate dictionary. Message payload definitions must conform to the following rules:

• attribute names must be unique within each message class
• attribute types must be one of the valid types (I1, U1, etc.)
• repeating groups are defined as nested dicts and must be preceded by an attribute which contains the number of repeats (see NAV-SVINFO by way of example). If this attribute is named 'numCh', the code will identity it automatically; if the attribute is given a different name, ubxmessage.py will need to be modified to identify it explicitly. If such an attribute is not present, the code will need to be modified to handle this particular message type as an exception to the norm e.g. deduce the number of repeats from the payload length.
• repeating attribute names are suffixed with a two-digit index (svid_01, svid_02, etc.)

Graphical Client

A python/tkinter graphical GPS client which supports both NMEA and UBX protocols (via pynmea2 and pyubx2 respectively) is under development at:

http://github.com/semuconsulting/PyGPSClient

Author Information

[e-mail]