geo.js

geo.js

//Source:
//https://code.google.com/p/geo-location-javascript/
var start_stop_btn, wpid = false,
    map, z, op, prev_lat, prev_long, min_speed = 0,
    max_speed = 0,
    min_altitude = 0,
    max_altitude = 0,
    distance_travelled = 0,
    min_accuracy = 150,
    date_pos_updated = "",
    info_string = "",
    latlng_string = "";

// This function just adds a leading "0" to time/date components which are <10 (because there is no cross-browser way I know of to do this using the date object)
function format_time_component(time_component) {
    if (time_component < 10) 
    	time_component = "0" + time_component;
    else if (time_component.length < 2) 
    	time_component = time_component + "0";

    return time_component;
}

// This is the function which is called each time the Geo location position is updated
function geo_success(position) {
    start_stop_btn.innerHTML = "Stop"; // Set the label on the start/stop button to "Stop"
    info_string = "";
    var d = new Date(); // Date object, used below for output messahe
    var h = d.getHours();
    var m = d.getMinutes();
    var s = d.getSeconds();

    var current_datetime = format_time_component(h) + ":" + format_time_component(m) + ":" + format_time_component(s);

    // Check that the accuracy of our Geo location is sufficient for our needs
    if (position.coords.accuracy <= min_accuracy) {
        // We don't want to action anything if our position hasn't changed - we need this because on IPhone Safari at least, we get repeated readings of the same location with 
        // different accuracy which seems to count as a different reading - maybe it's just a very slightly different reading or maybe altitude, accuracy etc has changed
        if (prev_lat != position.coords.latitude || prev_long != position.coords.longitude) {
            if (position.coords.speed > max_speed){ 
            	max_speed = position.coords.speed;
            }else if (position.coords.speed < min_speed){ 
            	min_speed = position.coords.speed;
            }

            if (position.coords.altitude > max_altitude){ 
            	max_altitude = position.coords.altitude;
            }else if (position.coords.altitude < min_altitude){ 
            	min_altitude = position.coords.altitude;
			}

            prev_lat = position.coords.latitude;
            prev_long = position.coords.longitude;

            info_string = "Current positon: lat=" + position.coords.latitude + ", long=" + position.coords.longitude + " (accuracy " + Math.round(position.coords.accuracy, 1) + "m)<br />Speed: min=" + (min_speed ? min_speed : "Not recorded/0") + "m/s, max=" + (max_speed ? max_speed : "Not recorded/0") + "m/s<br />Altitude: min=" + (min_altitude ? min_altitude : "Not recorded/0") + "m, max=" + (max_altitude ? max_altitude : "Not recorded/0") + "m (accuracy " + Math.round(position.coords.altitudeAccuracy, 1) + "m)<br />last reading taken at: " + current_datetime;
            latlng_string = position.coords.latitude + ',' + position.coords.longitude;
        }
    }else{
        info_string = "Accuracy not sufficient (" + Math.round(position.coords.accuracy, 1) + "m vs " + min_accuracy + "m) - last reading taken at: " + current_datetime;
    }

    if (info_string){
    	op.innerHTML = info_string;
    }
    	
    if (latlng_string){
    	$('#current').val(latlng_string);
    }
}

// This function is called each time navigator.geolocation.watchPosition() generates an error (i.e. cannot get a Geo location reading)
function geo_error(error) {
    switch (error.code) {
        case error.TIMEOUT:
            op.innerHTML = "Timeout!";
            break;
    };
}

function get_pos() {
    // Set up a watchPosition to constantly monitor the geo location provided by the browser - NOTE: !! forces a boolean response
    // We  use watchPosition rather than getPosition since it more easily allows (on IPhone at least) the browser/device to refine the geo location rather than simply taking the first available position
    // Full spec for navigator.geolocation can be foud here: http://dev.w3.org/geo/api/spec-source.html#geolocation_interface
    // First, check that the Browser is capable
    if (!!navigator.geolocation) {
        wpid = navigator.geolocation.watchPosition(geo_success, geo_error, {
            enableHighAccuracy: true,
            maximumAge: 30000,
            timeout: 27000
        });
    } else {
        op.innerHTML = "ERROR: Your Browser doesnt support the Geo Location API";
    }
}

// Initialiser: This will find the output message div and set up the actions on the start/stop button
function init_geo() {
    op = document.getElementById("output"); // Note the op is defined in global space and is therefore globally available
    if (op) {
        start_stop_btn = document.getElementById("geo_start_stop");

        if (start_stop_btn) {
            start_stop_btn.onclick = function() {
                if (wpid){ // If we already have a wpid which is the ID returned by navigator.geolocation.watchPosition(){
                    start_stop_btn.innerHTML = "Start";
                    navigator.geolocation.clearWatch(wpid);
                    wpid = false;
                }else{ // Else...We should only ever get here right at the start of the process
                    start_stop_btn.innerHTML = "Aquiring Geo Location...";
                    get_pos();
                }
            }
        }else{
            op.innerHTML = "ERROR: Couldn't find the start/stop button";
        }
    }
}

// Initialise the whole system (above)
window.onload = init_geo;