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NemaTode

Cross platform C++ 11 NMEA Parser & GPS Framework

NemaTode is yet another lightweight generic NMEA parser.

It also comes with a GPS data interface to handle the most popular GPS NMEA sentences.

Confirmed on MSVC 2013 and GCC 4.8.4.

It's too easy!

This is all you need to use the GPS NMEA sentence data.

NMEAParser parser;
GPSService gps(parser);
// (optional) Called when a sentence is valid syntax
parser.onSentence += [](const NMEASentence& nmea){
    cout << "Received $" << nmea.name << endl;
};
// (optional) Called when data is read/changed
gps.onUpdate += [](GPSService& gps){
    // There are *tons* of GPSFix properties
    if( gps.fix.locked() ){
        cout << " # Position: " << gps.fix.latitude << ", " << gps.fix.longitude << endl;
    } else {
        cout << " # Searching..." << endl;
    }
};
// Send in a log file or a byte stream
try {
    parser.readLine("FILL WITH A NMEA MESSAGE");
} catch (NMEAParseError&) {
    // Syntax error, skip
}

##Features

  • NMEA Parsing of standard and custom sentences.

    • Standard:
    GPGGA, GPGSA, GPGSV, GPRMC, GPVTG

  • NMEA Generation of "standard" and custom sentences.

    • SiRF Control sentences: PSRF100, PSRF103

  • GPS Fix class to manage and organize all the GPS related data.

  • Flexible

    • Stream data directly from a hardware byte stream
    • Read log files, even if they are cluttered with other unrelated data.
    • Easily hook into the parser to handle custom sentences and get their data.
    • Simplified GPS data

  • C++ 11 features

    • Those fancy event handlers...
    • If you are on an embedded system... sorry. This might not work for you because of compiler restrictions. Make sure there is full support for lambdas and variadic templates. Tested GCC 4.8.4, confirmed.

Details

NMEA is very popular with GPS. Unfortunately the GPS data is fragmented between many different NMEA sentences. Sometimes there is even conflicting information in them!

The underlying NMEAParser can read a byte stream from a hardware device or it can read log files with flexibility in the formatting. The accepted strings are...

"$[name:alphanum],[param[i]:alphanum],...(*alphanum[2]\r)\n"

The params allow '-' and any combination of whitespace.

The handler for "MYNMEA" is called. This is where you can catch the sentence and process it.

parser.setSentenceHandler("MYNMEA",[](const NMEASentence& nmea){
    if( ! nmea.checksumOK() ){
        // bad checksum, but valid syntax
    }
    if( nmea.parameters.size() < 3 ){
        // missing data, throw something.
        // catch it at the read*() call.
    }
    int mydata = parseInt(nmea.parameters[2]);
};

There are 2 ways to operate...

  • LAX It will eat anything.
    • Useful for reading log files.
    • Call readByte(), readBuffer(), readLine()
  • STRICT It will throw errors on anything that's not explicitly NMEA.
    • Call readSentence()

Demos

"demo_simple.cpp"

  • Just reads the GPS position data.

"demo_advanced.cpp"

  • Reads all the data
  • Sentence Generation
  • Custom Sentence handling

.

Generation

NMEACommand mycmd;
mycmd.name = "MYCMD";
mycmd.message = "your,data,csv";
string nmea = mycmd.toString();  // Creates: $MYCMD,your,data,csv*15

There are 2 included NMEACommands that can configure a GPS.

  • PSRF103 Configures message output ID and rate, and whether or not to use checksums.

  • PSRF100 Configures the UART serial connection (if the chip has one).

GPS Fix data available

Available data when all 5 GPS sentences are received. If some are missing then some parameters will never change from their default values. All data is checked for consistency. For example, visible satellites can never be less than the tracking satellites, etc.

GPSFix

GPSAlmanac     almanac;
GPSTimestamp 	timestamp;

char 		status;		// Status: A=active, V=void (not locked)
uint8_t 	type;		// Type: 1=none, 2=2d, 3=3d
uint8_t 	quality;	// Quality (1-6) 

double 		dilution;		// Combination of Vertical & Horizontal
double 		horizontalDilution;	// Horizontal dilution of precision, initialized to 10, best =1, worst = >20
double 		verticalDilution;	// Vertical is less accurate

double 		altitude;		// meters
double 		latitude;		// degrees N
double 		longitude;		// degrees E
double 		speed;			// km/h
double 		travelAngle;		// degrees true north (0-359)
int32_t 	trackingSatellites;
int32_t 	visibleSatellites;

bool 		locked();		// Whether or not the position is locked on, or accurate.
double 		horizontalAccuracy();	// Gets accuracy of position in meters
double 		verticalAccuracy();
bool 		hasEstimate();		// If no fix is available, this says the position data is close to a real fix.
	
std::chrono::seconds timeSinceLastUpdate();	// Returns time from last timestamp to right now, in seconds.

GPSSatellite

double 		snr;		// Signal-to-noise ratio. 0-99 dB
uint32_t 	prn;		// pseudo-random number.  (basically a satellite id)
double 		elevation;	// 0-90 deg
double 		azimuth;	// 0-359 deg

GPSAlmanac

std::vector<GPSSatellite> satellites;	// mapped by prn (id number)
double 		averageSNR(); 
double 		minSNR();
double 		maxSNR();
double 		percentComplete();	// if all the satellite information is loaded (0-100)

GPSTimestamp (UTC Time)

int32_t 	hour;		// Parsed values from GPS
int32_t 	min;		
double 		sec;		
int32_t 	month;		
int32_t 	day;		
int32_t 	year;		
double 		rawTime;	// Values collected directly from the GPS
int32_t 	rawDate;	
time_t 		getTime();	// Converts timestamp into Epoch time, seconds since 1/1/1970.

NemaTode?

NMEA -> ME -> EM -> NEMA

+Tode