Global Positioning System

The Global Positioning System (GPS) is a space-based statellite navigation system that provides location and time information on all weather conditions. It maintained by the US government and is freely accessible to anyone with a GPS receiver.

Here, we don't discuss its background, we want to know how to interpret the satellite positioning data.

1. There are a lot of GPS receivers in the market, we are using 3DR GPS MTK V2.0 now, as shown in Figure 1.



Figure 1: 3DR MTK V2.0


2. Connect GPS receiver to the Arduino Mega 2560.



Figure 2: Arduino Mega 2560


3. Next, wrie code to Arduino Mega 2560, the code very simple.
   
   void setup()
   {
     Serial.begin(38400);
     Serial1.begin(38400);
     Serial.flush();
     Serial1.flush();
   }
   void loop()
   {
     if(Serial1.available())
     {
       Serial.write(Serial1.read());
     }
   }
4. Open the COM port used by Arduino Mega 2560, you will see the received data from the GPS.
   
   $GPGGA,003121.200,0120.4690,N,10341.9579,E,1,4,2.63,-45.2,M,3.2,M,,*7E
   $GPGSA,A,3,22,31,25,14,,,,,,,,,2.81,2.63,0.99*0E
   $GPRMC,003121.200,A,0120.4690,N,10341.9579,E,0.00,151.76,080614,,,A*6F
   $GPVTG,151.76,T,,M,0.00,N,0.00,K,A*39
   $GPGGA,003121.400,0120.4690,N,10341.9579,E,1,4,2.63,-45.2,M,3.2,M,,*78
   $GPGSA,A,3,22,31,25,14,,,,,,,,,2.81,2.63,0.99*0E
   $GPRMC,003121.400,A,0120.4690,N,10341.9579,E,0.00,151.76,080614,,,A*69
   $GPVTG,151.76,T,,M,0.00,N,0.00,K,A*39
   $GPGGA,003121.600,0120.4690,N,10341.9579,E,1,4,2.63,-45.2,M,3.2,M,,*7A
   $GPGSA,A,3,22,31,25,14,,,,,,,,,2.81,2.63,0.99*0E
   $GPGSV,3,1,11,22,73,029,14,18,51,120,18,31,48,306,39,50,42,091,*7C
   $GPGSV,3,2,11,25,33,050,28,14,24,011,29,21,22,164,,16,14,205,*7D
   $GPGSV,3,3,11,29,11,117,,27,04,224,,193,,,*4B
   $GPRMC,003121.600,A,0120.4690,N,10341.9579,E,0.00,151.76,080614,,,A*6B
   $GPVTG,151.76,T,,M,0.00,N,0.00,K,A*39
   
   This is a part of GPS data, it looks terrible. Starting, you may feel very afraid, confused, don't know how to read it. But in fact, you can refer to the following web site, it explains the meaning of each of the data represented in detail.
   http://aprs.gids.nl/nmea/
   
   These data have been repeat and repeat, but what I need is the location, I want to know where I am, so we need to read $GPGGA this sentence.
   
   $GPGGA,003121.200,0120.4690,N,10341.9579,E,1,4,2.63,-45.2,M,3.2,M,,*7E

Name	Example data	Description
Sentence Identifier	$GPGGA	Global Positioning System Fix Data
Time	003121.200	00:31:21:200
Latitude	0120.4690, N	01° 20.4690' N or 01° 20' 28" 140''' N
Longitude	10341.9579, E	103° 41.9579' E or 103° 41' 57" 474''' E
Fix Quality: - 0 = Invalid - 1 = GPS fix - 2 = DGPS fix	1	Data is from a GPS fix
Number of Satellites	4	4 Satellites are in view
Horizontal Dilution of Precision (HDOP)	2.63	Relative accuracy of horizontal position
Altitude	-45.2, M	-45.2 meters above mean sea level
Height of geoid above WGS84 ellipsoid	3.2, M	3.2 meters
Time since last DGPS update	blank	No last updateZ
DGPS reference station id	blank	No station id
Checksum	*7E	Used by program to check for transmission errors

From the above table, know that I am at 01° 20' 28" 140 North and 103° 41' 57" 474 East.

Next, you can enter the location return by GPS receiver into the Google map: 1°20'28.140'' 103°41'57.474'' , it show that there is my home.