I’m working with an electron and working from an example using TinyGPS++ where they get the distance between two points. The examples with TinyGPS though use a fixed point, London, for one point and the current location pulled from the GPS. I’m attempting to capture a point and when I pull the next point 60 seconds later, I want to know the distance between the two points. My intent is that if the points are too close together that I will wait another 60 seconds and try again.
The coordinates that I am getting out seem to be right and I’m getting the same correct value at each iteration. But when I try to store the values to calculate distance, the values are changing significantly and the distanceBetween is returning many thousands of Kilometers. I think I am doing something simple wrong but I’m not spotting it, I’m hoping someone will spot it.
/*
Adapted from the example file "FullExample" included with the TinyGPS++ library
*/
#include <TinyGPS++/TinyGPS++.h>
// Change GPSBaud based on GPS unit
// 9600 for Adafruit's Ultimate GPS
static const uint32_t GPSBaud = 9600;
// The TinyGPS++ object
TinyGPSPlus gps;
char nullCoord[21];
// This custom version of delay() ensures that the gps object
// is being "fed".
static void smartDelay(unsigned long ms)
{
unsigned long start = millis();
do
{
while (Serial1.available())
gps.encode(Serial1.read());
} while (millis() - start < ms);
}
static void makeCoord(char *coord1, char *coord2, char *coords)
{
strcpy(coords,coord1);
strcat(coords,",");
strcat(coords,coord2);
}
void setup()
{
// Begin serial at 115200 Baud
Serial.begin(115200);
Serial.println(F("Hello world!"));
// Serial1 reads from the Electron's TX/RX
Serial1.begin(GPSBaud);
// Make the 0 coordinate
makeCoord("0.000000", "0.000000", nullCoord);
}
void loop()
{
// Now we prepare to publish location data to our webhook
// Make strings of the Latitude and Longitude readings
char coord1[10];
sprintf(coord1, "%f", (gps.location.lat(), gps.location.isValid(), 11, 6));
char coord2[10];
sprintf(coord2, "%f", (gps.location.lng(), gps.location.isValid(), 12, 6));
char speed[32];
sprintf(speed, "%ld", (gps.speed.mph(), gps.location.isValid()));
char course[32];
sprintf(course, "%ld", (gps.course.deg(), gps.location.isValid()));
// Combine these strings into the coordinate format accepted by Initial State
char curCoord[21];
makeCoord(coord1, coord2, curCoord);
// Send the data
if (strcmp(curCoord, nullCoord) != 0){
// Particle.publish("gpsData",curCoord);
}
// Save to last position variables
char lastCoord[21];
strcpy(lastCoord, curCoord);
double lastLat;
lastLat = gps.location.lat();
double lastLong;
lastLong = gps.location.lng();
double currLat;
double currLong;
char longchar[150];
sprintf(longchar, "last lat %d, last lng %d", lastLat, lastLong);
Serial.println(longchar);
// Wait 60 seconds
do {
smartDelay(60000);
currLat = gps.location.lat();
currLong = gps.location.lng();
sprintf(longchar, "GPS Lat %d, lng %d",currLat, currLong);
Serial.println(longchar);
Serial.println(TinyGPSPlus::distanceBetween(currLat, currLong, lastLat, lastLong));
} while (TinyGPSPlus::distanceBetween(currLat, currLong, lastLat, lastLong) < 100);
if (millis() > 5000 && gps.charsProcessed() < 10)
{
Serial.println(F("No GPS data received: check wiring"));
Particle.publish("gpsData",nullCoord);
}
}
I posted because it was confusing to me and I empathized with the OP … sorry I’ll fix things up! IIRC, the calculations work best when done in radians, and most GPS units spit out degrees easily so things work pretty naturally. But you must pay attention to what units you are working with, which is why the comments were meant to explain degrees are expected, and the formulas to convert between radians and degrees to help you recognize those patterns in case your LAT/LON has been pre-converted to radians.