DfAC/NMEAnoiseMaker

add artificial noise to NMEA string

NMEAnoiseMaker

This tool is adding artificial noise to NMEA string for equipment testing purpose. To generate synthetic NMEA string you can use https://www.nmeagen.org/

The National Marine Electronics Association (NMEA) has developed the interface specification between various marine electronic navigation equipment that permits to send information to computers and to other marine equipment. The standard is ASCII based and consist of series of predefined strings identifiable by the header.

• official gudelines can be purchased from https://www.nmea.org/
• description of most common geodetic NMEA-0183 strings can be found at https://www.trimble.com/OEM_ReceiverHelp/V4.44/en/NMEA-0183messages_MessageOverview.html

LKB 2019(c)

use example

• There is a sample nmea file in \data\ ; run python makeNMEAnoisy from code directory to see results - change allFiles = glob.glob('.\data\*.nmea') for different folders
• To use code in your project - from makeNMEAnoisy.py import createNoisyFile

workflow

createNoisyFile()

• reads $GPGGA
• create defined noise model precModel()
• output corrected $GPGGA with correct CRC - changeGGA()
• create $GPGST string based on $GPGGA, with correct CRC - createGST()
• read $GPRMC and match lat,lon with $GPGGA and add correct CRC; rest of the string remain unchanged - changeRMC() - this string is critical for GE - I am not altering other information here
• save everything as new file

NMEA strings

GGA

0	Message ID $GPGGA
1	UTC of position fix
2	Latitude
3	Direction of latitude: N: North,S: South
4	Longitude
5	Direction of longitude: E: East,W: West
6	GPS Quality indicator:
	0: Fix not valid
	1: GPS fix
	2: Differential GPS fix, OmniSTAR VBS
	4: Real-Time Kinematic, fixed integers
	5: Real-Time Kinematic, float integers, OmniSTAR XP/HP or Location RTK
7	Number of SVs in use, range from 00 through to 24+
8	HDOP
9	Orthometric height (MSL reference)
10	M: unit of measure for orthometric height is meters
11	Geoid separation
12	M: geoid separation measured in meters
13	Age of differential GPS data record, Type 1 or Type 9. Null field when DGPS is not used.
14	Reference station ID, range 0000-4095. A null field when any reference station ID is selected and no corrections are received1.
15	The checksum data, always begins with *

GST

0  Message ID $GPGST
1  UTC of position fix
2  RMS value of the pseudorange or carrier phase (RTK/PPP) residuals
3  Error ellipse semi-major axis 1 sigma error, in meters
4  Error ellipse semi-minor axis 1 sigma error, in meters
5  Error ellipse orientation, degrees from true north
6  Latitude 1 sigma error, in meters
7  Longitude 1 sigma error, in meters
8  Height 1 sigma error, in meters
9  The checksum data, always begins with *

RMC

0	Message ID $GPRMC
1	UTC of position fix
2	Status A=active or V=void
3	Latitude
4	Longitude
5	Speed over the ground in knots
6	Track angle in degrees (True)
7	Date
8	Magnetic variation in degrees
9	The checksum data, always begins with *