I am writing a distance tracker intended to track mileage for automobile drives with a mobile phone. I'm using cordova and cordova geolocation plugin. The code seems to run correctly where the geolocation plugin receives coordinates and I use the haversine formula to calculate the distance between two coordinates. However, my tracker is inaccurate because I am naively using lat/lon coordinates that are inaccurate. It appears that position has position.accuracy and position.speed. So I expect one or both of those properies may be useful.
accuracy: Accuracy level of the latitude and longitude coordinates in meters. (Number) speed: Current ground speed of the device, specified in meters per second. (Number)
My question is: are there known solutions for tracking distance that handle potentially inaccurate lat/lon information on a mobile phone?
More specific questions:
- How accurate does position.speed tend to be on mobile phones?
- Is there a position.accuracy that phones tend to gravitate towards? (I'm curious because I'm thinking of ignoring lat/lon cords with position.accuracy > threshold. So I'm trying to figure out what a good threshold would be)
Here's a snippet of my current code:
function DistanceTracker() {
this._currentPosition = null;
this.miles = 0.0;
}
DistanceTracker.prototype.start = function () {
var self = this;
navigator.geolocation.watchPosition(
/*success*/function (position) {
self.updateDistance(position);
},
/*fail*/function (errorPosition) {
//exception handling uses https://github.com/steaks/exceptions.js
throw new exceptions.Exception("Error in geolocation watchPosition", { data: errorPosition });
},
{ enableHighAccuracy: true, timeout: 5000 });
)
};
DistanceTracker.prototype.updateDistance = function (position) {
if (this._currentPosition !== null) {
this.miles = this.miles + this.getDistanceFromLatLonInMiles(
this._currentPosition.coords.latitude,
this._currentPosition.coords.longitude,
newPosition.coords.latitude,
newPosition.coords.longitude);
}
};
//Copied from http://stackoverflow.com/questions/27928/how-do-i-calculate-distance-between-two-latitude-longitude-points
function getDistanceFromLatLonInMiles(lat1,lon1,lat2,lon2) {
var R = 6371; // Radius of the earth in km
var dLat = deg2rad(lat2-lat1); // deg2rad below
var dLon = deg2rad(lon2-lon1);
var a =
Math.sin(dLat/2) * Math.sin(dLat/2) +
Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) *
Math.sin(dLon/2) * Math.sin(dLon/2)
;
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
var d = R * c; // Distance in km
return d * KILOMETERS_TO_MILES_RATIO;
}
function deg2rad(deg) {
return deg * (Math.PI/180);
}
