JSConf'14 Scavenger Hunt app

gistfile1.js

var card = new Pebble.UI.Card({ title: "JSConf 2014", subtitle: "Scavenger Hunt", scrollable: true });
card.show();

var msg = "Contacting NSA to get your current position ";
var timer = setInterval(function() {
  card.body(msg);
  msg += ".";
}, 800);

function distanceBetweenCoordinates(pos1, pos2) {
  var R = 6371; // Radius of the earth in km
  var dLat = (pos2.latitude - pos1.latitude) * (Math.PI/180);  // deg2rad below
  var dLon = (pos2.longitude - pos1.longitude) * (Math.PI/180);
  var a = 
    Math.sin(dLat/2) * Math.sin(dLat/2) +
    Math.cos((pos1.latitude) * (Math.PI/180)) * Math.cos(pos2.latitude * (Math.PI/180)) * 
    Math.sin(dLon/2) * Math.sin(dLon/2)
    ;
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
  var d = R * c * 1000; // Distance in m
  return d;
}

function angleBetweenCoords(pos1, pos2) {
  var dLon = (pos2.longitude - pos1.longitude);

  var y = Math.sin(dLon) * Math.cos(pos2.latitude);
  var x = Math.cos(pos1.latitude) * Math.sin(pos2.latitude) - Math.sin(pos1.latitude) * Math.cos(pos2.latitude) * Math.cos(dLon);

  var brng = Math.atan2(y, x);

  brng = brng * (180 / Math.PI);
  brng = (brng + 360) % 360;
  brng = 360 - brng;

  return brng;
}

var cardinals = {
  'N': [ 360 - 45/2, 360+45/2 ],
  'NE': [ 45 - 45/2, 45 + 45/2 ],
  'E' : [ 90 - 45/2, 90 + 45/2 ],
  'SE': [ 135 - 45/2, 135 + 45/2 ],
  'S':  [ 180 - 45/2, 180 + 45/2 ],
  'SW': [ 225 - 45/2, 225 + 45/2 ],
  'W':  [ 270 - 45/2, 270 + 45/2 ],
  'NW': [ 315 - 45/2, 315 + 45/2 ]
};

function angleToCardinal(angle) {
  console.log("AngleToCardinals: " + angle);
  for (var k in cardinals) {
    if (angle >= cardinals[k][0] && angle <= cardinals[k][1]) {
      return k;
    }
  }
  return "???";
}

var targetCoords = { latitude: 30.5625, longitude: -81.453611 };

var foundTree = false;

function gotPosition(pos) {
  clearInterval(timer);
  var distance = distanceBetweenCoordinates(pos.coords, targetCoords);
  var angle = angleBetweenCoords(pos.coords, targetCoords);

  console.log("Got Position: " + JSON.stringify(pos));
  console.log("Distance: " + distance + " Angle: " + angle);
  if (distance > 20) {
    card.body("You are " + Math.round(distance) + "m from the goal! Direction: " + angleToCardinal(angle));
    foundTree = false;
  } else {
    card.body("Good! You made it! Take a picture of your team with the 'Landmark Oak'\n\nThis demo was built entirely in JS - Check the source on pbl.io/jsconfscavengersource");
  }
}

function positionError(err) {
  clearInterval(timer);
  console.log("Unable to get coordinates ... :( " + err.code + " " + err.message);
  card.body("NSA does not like you ... No luck with GPS.");
}

setTimeout(function() {
  navigator.geolocation.watchPosition(gotPosition, positionError, { enableHighAccuracy: true, maximumAge: 0 });
}, 3000);