This example illustates basic use of the NMEA library. It assumes that a GPS receiver is connected to serial port 'Serial1' at 4800 bps, and that a LED is connected to digital i/o pin 0.

A GPS data connection of type GPRMC is created, and used to get position information. When the GPS position is in the state of Colorado (USA), the LED lights up, otherwise it is off.

 
#include <nmea.h>

// create a GPS data connection to GPRMC sentence type
NMEA gps(GPRMC);

void setup() {
  Serial1.begin(4800);
  pinMode(0, OUTPUT);
}

void loop() {
  if (Serial1.available() > 0 ) {
    // read incoming character from GPS
    char c = Serial1.read();

    // check if the character completes a valid GPS sentence
    if (gps.decode(c)) {
      // check if GPS positioning was active
      if (gps.gprmc_status() == 'A') {
        // check if you are in Colorado, USA
        boolean inColorado = (gps.gprmc_latitude() > 37.0)
                          && (gps.gprmc_latitude() < 41.0)
                          && (gps.gprmc_longitude() < -102.05)
                          && (gps.gprmc_longitude() > -109.05);

        // set led accordingly
        if (inColorado) {
          digitalWrite(0, HIGH);
        } else {
          digitalWrite(0, LOW);
        }
      }
    }
  }
}