Gps Coordinate conversion help

Projects Programming
1

Hi guys,

A bit of background info: i've made a information display unit for my 4 wheel drive, that displays among other things, Latitude and Longitude in decimal degrees, Eg, -36.76453, 145.74653.. but i if need to convert this info to Degrees, Minutes, Seconds, eg -36° 76' 53, 145° 74' 53. i know i need to do some maths, here's an example of how to do it i found.

DM.m = Degrees, Minutes, Decimal Minutes (eg. 45°22.6333)
D.d = Degrees, Decimal Degrees (eg. 45.3772°)
DMS = Degrees, Minutes, Seconds (eg. 45°22'38")

D.d --> DM.m (45.3772 --> 45°22.6333
Multiply .d by 60 to get M.m (.3772*60=22.6333)

DM.m --> DMS (45°22.6333 --> 45°22'38")
Multiply .m by 60 to get S(.6333*60=38)

My question is: how do i put this in my sketch?

I know i need to use the "Latitude" and "Longitude" values and use the above method to convert it before sending it to the LCD. i hope that makes sense.

// necessary libraries
#include <TinyGPS.h> //GPS
#include <LiquidCrystal.h>
#include <OneWire.h> //for temp sensor
#include <Wire.h>
#include <LSM303DLH.h> //compass
#include <DHT.h> //temp humidity sensor

#define DHTPIN 30 // DHT sensor pin
#define DHTTYPE DHT22 // DHT 22 (AM2302)
DHT dht(DHTPIN, DHTTYPE);

LSM303DLH compass;

const int heading_min = 0; // sensor minimum,
const int heading_max = 359;

// The parameters in the brackets define which digital output pins connect to
// (in order) LCD pins: RS, enable, D4, D5, D6, and D7.
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
LiquidCrystal lcd2(12, 10, 5, 4, 3, 2); //second display

//---------------------------GPS------------------------------------------------------
#define GPSBAUD 9600 // baud rate of our GPS module. Change for your GPS module if different
TinyGPS gps; // Create an instance of the TinyGPS object
void getgps(TinyGPS &gps); // This is where you declare prototypes for the functions that will be
// using the TinyGPS library.

Serial1.begin(GPSBAUD); // setup sketch for data output speed of GPS module

lcd.begin(20, 4);
lcd2.begin(20, 4);

lcd.clear();
//lcd2.clear();

lcd.setCursor(2,1);
lcd.print("Waiting for lock");

}

void loop()

{

GPS_LOC ( );
Batt_V_I ( );
OutTemp ( );
Compass ( );
TempHumidSensor ( );

}

int GPS_LOC( )

{

while(Serial1.available()) // While there is data on the RX pin...
{
int c = Serial1.read(); // load the data into a variable...
if(gps.encode(c)) // if there is a new valid sentence...

{
getgps(gps); // then grab the data.
}
}
}

void getgps(TinyGPS &gps) // The getgps function will get and print the values we want.

{

float latitude, longitude, fix_age; // Define the variables that will be used

gps.f_get_position(&latitude, &longitude); // You can now print variables latitude and longitude

lcd.clear();

lcd.setCursor(0,0);
lcd.print("Latitude : "); lcd.print(latitude,5);

lcd.setCursor(0,1);
lcd.print("Longitude: "); lcd.print(longitude,5);

lcd.setCursor(0,2);
lcd.print("Altitude : ");
lcd.print(gps.f_altitude());lcd.print("m");

lcd.setCursor(0,3);
lcd.print("Speed: ");
lcd.print(gps.f_speed_kmph(),0); //lcd.print("k");

lcd.setCursor(11,3);
lcd.print("Sats: ");
lcd.print(gps.satellites());

//Serial.print("HDOP: "); Serial.println(gps.hdop());

}

(had to delete some of my sketch to make it fit in this post)

Thanks for helping!

2

http://williams.best.vwh.net/avform.

pay attention, arduino's 32 bit float give some unprecise result. take a look at bignumber library

3

thanks, but thats not what i'm having trouble with

4

What's the source of your longitude/latitude readings? most gps modules give reading in degrees only, ie:
145.74653 is not 145 degrees 74' 65". It's 145.74653 degrees.

It's up to you to convert .74653 degrees into minutes and seconds. There are 60 minutes in a degree, and 60 seconds in a minute, or 3600 seconds in a degree, so .74653 degrees = 2687 seconds (or 44 minutes, 47 seconds)

5

Firstly the 24 bit resolution of floating point may not be sufficient for a GPS Lat/Lon value. Better to use a fixed-point representation, such as using a long int that is a count of millionths of a degree.

Thus 123.45678 degrees would be represented by 123456780L (L for long). The kind of code to do the conversion progresses from degrees through minutes to seconds and fractions of a second - this is generalized base-conversion and a straightforward way for this case might look like:

  long micro_degrees = 123456789L ;
  int  degrees = micro_degrees / 1000000L ;      // degrees = 123
  micro_degrees -= 1000000L * degrees ;          // micro_degrees = 456789
  long  milli_minutes = micro_degrees * 3 / 50 ; // miili_minutes = 27407
  int minutes = milli_minutes / 1000 ;           // minutes = 27
  milli_minutes -= 1000L * minutes ;             // milli_minutes = 407
  int centi_seconds = milli_minutes * 6 ;        // centi_seconds = 2442
  int seconds = deci_seconds / 10 ;              // seconds = 24
  centi_seconds -= 10 * seconds ;                // centi_seconds = 42

So you get 123 deg, 27 minutes, 24.42 seconds (back check gives 123.456783 degrees, about 2 feet out.

6

jraskell. i get the readings from the gps, which i print the latitude and longitude like you said, to 5 decimal places

float latitude, longitude, fix_age; // Define the variables that will be used

gps.f_get_position(&latitude, &longitude); // You can now print variables latitude and longitude

lcd.clear();

lcd.setCursor(0,0);
lcd.print("Latitude : "); lcd.print(latitude,5); // Print to LCD to 5 decimal places.

lcd.setCursor(0,1);
lcd.print("Longitude: "); lcd.print(longitude,5);

so i know i have to use the 'latitude,5'

MarkT.. could i use your example and replace first line with "long micro_degrees = (latitude,5);" ?

7

long are number without decimal, so decimal part is truncated. if you want to save 5 decimal, just do

long micro_degrees = latitude*10000;
8

You just need to set micro_degrees to the (long integer) number of micro-degrees. Made tricky by the fact that a float isn't accurate enough - you can read the part before and after the decimal point as integers and combine them. An exercise in arithmetic.

9

hey MarkT..

im not very good at maths, i think i even failed it in high school!

would this be how i could get it to work?

long micro_degrees = latitude;
int degrees = micro_degrees / 1000000L ; // degrees = 123
micro_degrees -= 1000000L * degrees ; // micro_degrees = 456789
long milli_minutes = micro_degrees * 3 / 50 ; // miili_minutes = 27407
int minutes = milli_minutes / 1000 ; // minutes = 27
milli_minutes -= 1000L * minutes ; // milli_minutes = 407
int centi_seconds = milli_minutes * 6 ; // centi_seconds = 2442
int seconds = deci_seconds / 10 ; // seconds = 24
centi_seconds -= 10 * seconds ; // centi_seconds = 42

lcd.print (micro_degrees);

i feel like i'm missing something....?