pyspartn 0.2.1

SPARTN protocol parser

pyspartn

Current Status | Installation | Reading | Parsing | Generating | Serializing | Examples | Graphical Client | Author & License

pyspartn is an original Python 3 parser for the SPARTN © GPS/GNSS protocol. SPARTN is an open-source GPS/GNSS differential correction or DGPS protocol published by u-blox.

SPARTN Protocol 2.01 (available in the public domain). © 2021 u-blox AG. All rights reserved.

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

This is an independent project and we have no affiliation whatsoever with u-blox.

FYI There are companion libraries which handle standard NMEA 0183 ©, UBX © (u-blox) and RTCM3 © GNSS/GPS messages:

• pyubx2 (FYI installing pyubx2 via pip also installs pynmeagps and pyrtcm)
• pynmeagps
• pyrtcm

Current Status

WORK IN PROGRESS - CURRENTLY IN ALPHA.

The SPARTNReader class is fully functional and is capable of parsing individual SPARTN transport-layer messages from a binary data stream containing solely SPARTN data, with their associated metadata (message type/subtype, payload length, encryption parameters, etc.).

The SPARTNMessage class implements a provisional decrypt and decode for OCB, HPAC and GAD message types but it has not yet been fully tested (appears to be working OK for GAD, HPAC and most OCB payloads, but some small OCB payloads (nData < 35) are still failing. For the time being, a temporary override has been implemented in spartnmessage.py to suppress the decode flag for those payload types that cannot yet be successfully decoded).

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

Contributions welcome - please refer to CONTRIBUTING.MD.

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

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Installation

pyspartn is compatible with Python >=3.8 and is dependent on the cryptography library.

NB: If you're installing pyspartn on a 32-bit Linux platform, some additional installation steps may be required - see note ¹ below.

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 pyspartn is with pip:

python3 -m pip install --upgrade pyspartn

If required, pyspartn 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 pyspartn
...
deactivate

¹ On some 32-bit Linux platforms (e.g. Raspberry Pi OS 32), it may be necessary to install Rust compiler support in order to install the cryptography library which pyspartn depends on to decrypt SPARTN messages (see Discussion):

See cryptography install README.

For Conda users, pyspartn is also available from conda-forge:

conda install -c conda-forge pyspartn

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Reading (Streaming)

class pyspartn.spartnreader.SPARTNReader(stream, **kwargs)

You can create a SPARTNReader 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). pyspartn implements an internal SocketStream class to allow sockets to be read in the same way as other streams (see example below).

Individual SPARTN messages can then be read using the SPARTNReader.read() function, which returns both the raw binary data (as bytes) and the parsed data (as a SPARTNMessage, via the parse() method). The function is thread-safe in so far as the incoming data stream object is thread-safe. SPARTNReader also implements an iterator.

Example - Serial input:

>>> from serial import Serial
>>> from pyspartn import SPARTNReader
>>> stream = Serial('/dev/tty.usbmodem14101', 9600, timeout=3)
>>>spr = SPARTNReader(stream)
>>> (raw_data, parsed_data) = spr.read()
>>> print(parsed_data)

Example - File input (using iterator).

>>> from pyspartn import SPARTNReader
>>> stream = open('spartndata.log', 'rb')
>>> spr = SPARTNReader(stream)
>>> for (raw_data, parsed_data) in spr: print(parsed_data)
...

Example - Socket input (using iterator):

>>> import socket
>>> from pyspartn import SPARTNReader
>>> stream = socket.socket(socket.AF_INET, socket.SOCK_STREAM):
>>> stream.connect(("localhost", 50007))
>>> spr = SPARTNReader(stream)
>>> for (raw_data, parsed_data) in spr: print(parsed_data)

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Parsing

You can parse individual SPARTN messages using the static SPARTNReader.parse(data) function, which takes a bytes array containing a binary SPARTN message and returns a SPARTNMessage object. The optional decode keyword argument signifies whether to decrypt and decode the full payload (default = False). If decode is set to True and the message is encrypted (eaf=1), you must provide the following arguments:

• key - the SPARTN decryption key valid at the time the message was originally created, as provided by your SPARTN service (normally 32 hexadecimal characters).
• basedate - a nominal datetime or 32-bit gnssTimeTag value, needed to convert an ambiguous 16-bit gnssTimeTag value to its unambiguous 32-bit equivalent. This is used by the decryption routine to determine the cryptographic Initialisation Vector (IV). If you're parsing messages in real time, this can default to datetime.now(). If you're parsing data from an older message stream, you will need to use the datetime the stream was originally created (to the nearest half day), or a 32-bit gnssTimeTag value from the same stream. See examples below.

NB: Once instantiated, a SPARTNMMessage object is immutable.

Example - without payload decryption:

>>> from pyspartn import SPARTNReader
>>> msg = SPARTNReader.parse(b"s\x00\x12\xe2\x00|\x10[\x12H\xf5\t\xa0\xb4+\x99\x02\x15\xe2\x05\x85\xb7\x83\xc5\xfd\x0f\xfe\xdf\x18\xbe\x7fv \xc3`\x82\x98\x10\x07\xdc\xeb\x82\x7f\xcf\xf8\x9e\xa3ta\xad", decode=False)
>>> print(msg)
<SPARTN(SPARTN-1X-OCB-GPS, msgType=0, msgSubtype=0, nData=37, eaf=1, crcType=2, frameCrc=2, timeTagtype=0, gnssTimeTag=3970, solutionId=5, solutionProcId=11)>

Example - with payload decryption (requires key and, for messages where timeTagtype = 0, a nominal basedate for IV calculation):

>>> from pyspartn import SPARTNReader
>>> from datetime import datetime
>>> msg = SPARTNReader.parse(b'\x73\x04\x19\x62\x03\xfa\x20\x5b\x1f\xc8\x31\x0b\x03\xd3\xa4\xb1\xdb\x79\x21\xcb\x5c\x27\x12\xa7\xa8\xc2\x52\xfd\x4a\xfb\x1a\x96\x3b\x64\x2a\x4e\xcd\x86\xbb\x31\x7c\x61\xde\xf5\xdb\x3d\xa3\x2c\x65\xd5\x05\x9f\x1c\xd9\x96\x47\x3b\xca\x13\x5e\x5e\x54\x80', decode=True, key="6b30302427df05b4d98911ebff3a4d95", basedate=datetime(2023,6,27,22,3,0))
                                                                               
>>> print(msg)
<SPARTN(SPARTN-1X-GAD, msgType=2, nData=50, eaf=1, crcType=2, frameCrc=2, msgSubtype=0, timeTagtype=0, gnssTimeTag=32580, solutionId=5, solutionProcId=11, encryptionId=1, encryptionSeq=63, authInd=1, embAuthLen=0, crc=6182016, SF005=37, SF068=1, SF069=0, SF030=7, SF031_01=32, SF032_01=1332, SF033_01=1987, SF034_01=6, SF035_01=2, SF036_01=5, SF037_01=22, SF031_02=33, SF032_02=1332, SF033_02=2033, SF034_02=6, SF035_02=3, SF036_02=5, SF037_02=16, SF031_03=34, SF032_03=1301, SF033_03=1921, SF034_03=2, SF035_03=6, SF036_03=18, SF037_03=10, SF031_04=35, SF032_04=1297, SF033_04=1987, SF034_04=3, SF035_04=3, SF036_04=12, SF037_04=22, SF031_05=36, SF032_05=1448, SF033_05=1768, SF034_05=6, SF035_05=2, SF036_05=5, SF037_05=30, SF031_06=37, SF032_06=1391, SF033_06=1745, SF034_06=4, SF035_06=7, SF036_06=7, SF037_06=10, SF031_07=38, SF032_07=1360, SF033_07=1906, SF034_07=3, SF035_07=2, SF036_07=8, SF037_07=22)>

The SPARTNMessage object exposes different public attributes depending on its message type or 'identity'. SPARTN data fields are denoted SFnnn - use the datadesc() helper method to obtain a more user-friendly text description of the data field.

>>> from pyspartn import SPARTNReader, datadesc
>>> msg = SPARTNReader.parse(b'\x73\x03\x35\xec\x08\xc7\xd4\x20\x70\x5b\x1f\xc ... \x1e\xbe\x18\x43\x2d\x57\xe7\xa7', decode=True, key="00112233445566778899aabbccddeeff")
>>> print(msg)
<SPARTN(SPARTN-1X-HPAC-GPS, msgType=1, nData=619, eaf=1, crcType=2, frameCrc=12, msgSubtype=0, timeTagtype=1, gnssTimeTag=419070990, solutionId=5, solutionProcId=11, encryptionId=1, encryptionSeq=63, authInd=1, embAuthLen=0, crc=5760935, SF005=508, SF068=1, SF069=0, SF030=9, SF031_01=0, SF039_01=0, SF040T_01=1, SF040I_01=1, SF041_01=1, SF042_01=2, SF043_01=127, SF044_01=1, SF048_01=213, SF049a_01=257, SF049b_01=253, SF054_01=1, SatBitmaskLen_01=0, SF011_01=70263185, SF055_01_01=6, SF056_01_01=1, SF060_01_01=8944, ... SF061b_09_08=8287)>
>>> msg.identity
'SPARTN-1X-HPAC-GPS'
>>> msg.gnssTimeTag
419070990
>>> msg.SF005
508
datadesc("SF005")
'Solution issue of update (SIOU)'

The payload attribute always contains the raw payload as bytes.

---

Generating

class pyspartn.spartnmessage.SPARTNMessage(**kwargs)

You can create an SPARTNMessage object by calling the constructor with the following keyword arguments:

1. transport as bytes

Example:

>>> from pyspartn import SPARTNMessage
>>> msg = SPARTNMessage(transport=b"s\x00\x12\xe2\x00|\x10[\x12H\xf5\t\xa0\xb4+\x99\x02\x15\xe2\x05\x85\xb7\x83\xc5\xfd\x0f\xfe\xdf\x18\xbe\x7fv \xc3`\x82\x98\x10\x07\xdc\xeb\x82\x7f\xcf\xf8\x9e\xa3ta\xad")
>>> print(msg)
<SPARTN(SPARTN-1X-OCB-GPS, msgType=0, msgSubtype=0, nData=37, eaf=1, crcType=2, frameCrc=2, timeTagtype=0, gnssTimeTag=3970, solutionId=5, solutionProcId=11)>

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Serializing

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

e.g. to create and send a 1005 message type:

>>> from serial import Serial
>>> serialOut = Serial('COM7', 38400, timeout=5)
>>> from pyspartn import SPARTNMessage
>>> msg = SPARTNMessage(transport=b"s\x00\x12\xe2\x00|\x10[\x12H\xf5\t\xa0\xb4+\x99\x02\x15\xe2\x05\x85\xb7\x83\xc5\xfd\x0f\xfe\xdf\x18\xbe\x7fv \xc3`\x82\x98\x10\x07\xdc\xeb\x82\x7f\xcf\xf8\x9e\xa3ta\xad")
>>> print(msg)
<SPARTN(SPARTN-1X-OCB-GPS, msgType=0, msgSubtype=0, nData=37, eaf=1, crcType=2, frameCrc=2, timeTagtype=0, gnssTimeTag=3970, solutionId=5, solutionProcId=11)>
>>> output = msg.serialize()
>>> output
b"s\x00\x12\xe2\x00|\x10[\x12H\xf5\t\xa0\xb4+\x99\x02\x15\xe2\x05\x85\xb7\x83\xc5\xfd\x0f\xfe\xdf\x18\xbe\x7fv \xc3`\x82\x98\x10\x07\xdc\xeb\x82\x7f\xcf\xf8\x9e\xa3ta\xad"
>>> serialOut.write(output)

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Examples

The following examples are available in the /examples folder:

1. rxmpmp_extract_spartn.py - ilustrates how to extract individual SPARTN messages from the accumulated UBX-RXM-PMP data output by an NEO-D9S L-band correction receiver.
2. spartnparser.py - illustrates how to parse SPARTN transport layer data from the binary SPARTN messages output by the example above.
3. gad_plot.py - illustrates how to extract geographic area definitions from a series of SPARTN-GAD-1X messages - the output file from the example above can be used as an input. This example also serves to illustrate how to decrypt SPARTN messages.

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Graphical Client

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

https://github.com/semuconsulting/PyGPSClient

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Author & License Information

[e-mail]

pyspartn is maintained entirely by unpaid volunteers. It receives no funding from advertising or corporate sponsorship. If you find the library useful, a small donation would be greatly appreciated!