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Addition of big decimal values in javascript for calculating distance on google map

I am a fresher in coding and working on web designing on googlemap. I have a problem in finding total distance covered by user because i am using a formula for finding distance and then adding this distance one by one.The distance is like 0.41384640620101654 so when i am adding number of values of this type it is giving 0 or error.
here is my code
getDistance();
var mn = 0.00;
function getDistance()
{
for (var i = 0; i < polyline_data.length-1; i++)
{
$lngfrom = polyline_data[i].lng;
$lngto = polyline_data[i+1].lng;
$latfrom = polyline_data[i].lat;
$latto = polyline_data[i+1].lat;
$theta = $lngfrom - $lngto;
var pi = Math.PI;
var x = $latfrom * (pi/180);
var y = $latto * (pi/180);
var z = $theta * (pi/180);
var dist = new Array();
var distance = Math.sin(x) * Math.sin(y)+ Math.cos(x) * Math.cos(y) * Math.cos(z);
distance = Math.acos(distance);
distance = distance*(180/pi);
var miles = distance * 60 * 1.8515;
distance = miles * 1.609344;
distance = parseFloat(distance);
//distance = Math.round(distance);
//dist = dist.push(distance);
//distance+=distance;
console.log(distance);
//console.log(all);
//console.log(distance);
}
//var all = new Array();
//for(j=0;j<polyline_data.length-1;j++)
//{
//all[j]=distance;
//}
//console.log(all);
}

Geolocation doesn't update my walked distance

Hi I'm creating an walk tracker webapp by usiing geolocation with javascript. Everything works fine except the part when I have to calculate the distance by using the old latlong with new latlong.
The Code:
function updateLocation(position) {
var latitude = position.coords.latitude;
var longitude = position.coords.longitude;
var accuracy = position.coords.accuracy;
var timestamp = position.timestamp;
document.getElementById("latitude").innerHTML = latitude;
document.getElementById("longitude").innerHTML = longitude;
document.getElementById("accuracy").innerHTML = accuracy.toFixed(2) + " meter";
document.getElementById("timestamp").innerHTML = new Date(timestamp).toLocaleString();
if (accuracy >= 500) {
updateStatus("Need more accurate values to calculate distance.");
return;
}
if ((lastLat != null) && (lastLong != null)) {
var currentDistance = distance(latitude, longitude, lastLat, lastLong);
document.getElementById("currDist").innerHTML =
"Current distance traveled: " + currentDistance.toFixed(2) + " km";
totalDistance += currentDistance;
document.getElementById("totalDist").innerHTML =
"Total distance traveled: " + currentDistance.toFixed(2) + " km";
}
lastLat = latitude;
lastLong = longitude;
updateStatus("Location successfully updated.");
}
Added the distance function*
Number.prototype.toRadians = function() {
return this * Math.PI / 180;
}
function distance(latitude1, longitude1, latitude2, longitude2) {
// R is the radius of the earth in kilometers
var R = 6371;
var deltaLatitude = (latitude2-latitude1).toRadians();
var deltaLongitude = (longitude2-longitude1).toRadians();
latitude1 = latitude1.toRadians(), latitude2 = latitude2.toRadians();
var a = Math.sin(deltaLatitude/2) *
Math.sin(deltaLatitude/2) +
Math.cos(latitude1) *
Math.cos(latitude2) *
Math.sin(deltaLongitude/2) *
Math.sin(deltaLongitude/2);
var c = 2 * Math.atan2(Math.sqrt(a),
Math.sqrt(1-a));
var d = R * c;
return d;
}
Hope someone can find what Im doing wrong.
Thank you
Update:
I found the problem why geolocation didn't update my distance.. it's because the variable lastlong and lastlat which I declared didn't gave me the previous location, it gave me the current location of latitude and longitude which I declared inside updateLocation and assign lastlat and last long with those variable.
My question is now how can I calculate the previous location with the
new location, can't find any solution for it.
New Update:
Found my solution for this problem. For calculating the previous
distance I store the coords in a array and get the last position to
calculate the distance with the current position.
Code:
var coords = []; var distance = 0.0;
function calculateDistance(fromPos, toPos) {
var radius = 6371;
var toRad = function(number) {
return number * Math.PI / 180;
};
var latDistance = toRad(toPos.latitude - fromPos.latitude);
var lonDistance = toRad(toPos.longitude - fromPos.longitude);
var a = Math.sin(latDistance / 2) * Math.sin(latDistance / 2) +
Math.cos(toRad(fromPos.latitude)) * Math.cos(toRad(toPos.latitude)) *
Math.sin(lonDistance / 2) * Math.sin(lonDistance / 2);
return radius * (2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a)));
}
var lastPos = coords[coords.length-1];
if(lastPos) {
distance += calculateDistance(lastPos, position.coords);
document.getElementById("currDist").innerHTML =
"Current distance traveled: " + distance.toFixed(2) + " km";
}
coords.push(position.coords);
One thing that I not understand is why my timestamp inside my array is undefined? Because the lat and long can I get easy without problem.

For a complete working journey logger example please see Google Drive or GitHub.
Pay attention to the filterLocation function in TravelManagerPolyfil.js as you might just be getting many zero distance readings and need to throttle watchPosition.
This code works: -
<!DOCTYPE html>
<html>
<body>
<p>Click the button to get your coordinates.</p>
<button onclick="getLocation()">Try It</button>
<p id="demo"></p>
<script>
var perthLat = 31.9505;
var perthLon = 115.8605;
var freoLat = 32.0569;
var freoLon = 115.7439;
const EARTH_RADIUS = 6378137;
var toRad =
function (num) {
return num * Math.PI / 180;
};
var calculateDistance =
function(lat1, lon1, lat2, lon2){
var dLat = toRad(lat2 - lat1);
var dLon = toRad(lon2 - lon1);
var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.cos(this.toRad(lat1)) *
Math.cos(toRad(lat2)) * Math.sin(dLon / 2) * Math.sin(dLon / 2);
var distance = EARTH_RADIUS * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
return distance;
}
var x = document.getElementById("demo");
function getLocation() {
if (navigator.geolocation) {
navigator.geolocation.getCurrentPosition(showPosition);
} else {
x.innerHTML = "Geolocation is not supported by this browser.";
}
}
function showPosition(position) {
x.innerHTML = "Distance = " +
calculateDistance(perthLat, perthLon,
freoLat, freoLon) / 1000;
}
</script>
</body>
</html>

select marker using google maps and leap motion

I have been trying to select a marker on google maps closest to the leap motion coordinate. I have tried converting the leap motion coordinate to google maps coordinate and find the closest marker on google maps to the leap motion device by doing marker.lat and marker.lng for the markers compared to the lat and longitude calculated. However, it isn't working instead it is returning the marker at the bottom of the screen or the top of the screen. Here is my current javaScript code.
var results = document.getElementById('resultsTable');
console.log("Key Tap Gesture at: " + keyTapGesture.position[0]);
//google.maps.event.dispatchEvent(ktEvent);
var closestMarkerDistance = 10000000000000000000000000; //big number to start, so any calculation will override this value
var closestMarker = null;
var distance = 10000000000000000000000000;
console.log("marker distances to keytap are: " + results.length);
var hand = frame.hands[0];
var stabilized = hand.stabilizedPalmPosition;
for (var i = 0; i < markers.length; i++) {
var markerPos = 0;
var keyTapX = 0;
var keyTapY = 0;
var newLatLngPt = 0;
var keyLng = 0;
var keyLat = 0;
markerPos = markers[i].position;
keyTapX = stabilized[0];
keyTapY = stabilized[1];
newLatLngPt = convertToLatLng(keyTapX, keyTapY);
var scaling = 4.0 / Math.pow(2, map.getZoom() - 1);
keyLng = keyTapX * scaling;
keyLat = keyTapY * scaling;
//var keyTapCoord = new google.maps.LatLng(keyLat, keyLng);
distance = getDistanceFromLatLonInKm(markerPos.lat(), markerPos.lng(), newLatLngPt.lat(), newLatLngPt.lng());
if (distance < closestMarkerDistance) {
closestMarkerDistance = distance;
closestMarker = markers[i];
}
console.log(" \n" + distance + markers[i].getTitle());
}
if(closestMarker != null) {
console.log("\nclosest marker is : " + closestMarker.name + " title: " + closestMarker.getTitle() + " at pos: " + closestMarker.getPosition());
infowindow.setContent(closestMarker.getTitle());
infowindow.open(map,closestMarker);
console.log("\n ALSO: --> " + stabilized[0] + " ::::::" + stabilized[1]);
console.log("\n ANNNNNND: --> " + keyLng + " ::::::" + keyLat + "and then real la/lo = " + markerPos.lng() + " ____ " + markerPos.lat());
//document.getElementById(choices).innerHTML = place.name + "<br/>" + place.vicinity;
}
else {
console.log("\nclosest marker Does Not Exist");
}
function getDistanceFromLatLonInKm(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;
}
function convertToLatLng(x, y) {
// retrieve the lat lng for the far extremities of the (visible) map
var latLngBounds = map.getBounds();
var neBound = latLngBounds.getNorthEast();
var swBound = latLngBounds.getSouthWest();
// convert the bounds in pixels
var neBoundInPx = map.getProjection().fromLatLngToPoint(neBound);
var swBoundInPx = map.getProjection().fromLatLngToPoint(swBound);
// compute the percent of x and y coordinates related to the div containing the map; in my case the screen
var procX = x / window.innerWidth;
var procY = y / window.innerHeight;
// compute new coordinates in pixels for lat and lng;
// for lng : subtract from the right edge of the container the left edge,
// multiply it by the percentage where the x coordinate was on the screen
// related to the container in which the map is placed and add back the left boundary
// you should now have the Lng coordinate in pixels
// do the same for lat
var newLngInPx = (neBoundInPx.x - swBoundInPx.x) * procX + swBoundInPx.x;
var newLatInPx = (swBoundInPx.y - neBoundInPx.y) * procY + neBoundInPx.y;
// convert from google point in lat lng and have fun :)
var newLatLng = map.getProjection().fromPointToLatLng(new google.maps.Point(newLngInPx, newLatInPx));
return newLatLng;
}
function deg2rad(deg) {
return deg * (Math.PI / 180)
}

The Leap Motion coordinate system has nothing to do with your browser window. The X axis extends from approx. -300mm to +300mm. The Y axis extends from about 0 to +600mm -- it also is positive upward, while your browser Y-axis is more positive downward. If I read your code correctly, you are trying to use the Leap Motion coordinates as if they were pixel coordinates. They aren't.
You need to map the Leap Motion coordinates to something that makes sense for your application. This article in the documentation may help: https://developer.leapmotion.com/documentation/javascript/devguide/Leap_Coordinate_Mapping.html
In particular, have a look at the InteractionBox class, with which you can normalize the Leap Motion coordinates to the range [0..1]. It is generally easier to map the normalized coordinates to your application coordinate system.

Javascript Multiple Asynchronous setInterval

I'm trying to write code to track real-time positions of roughly 100 vehicles via GPS. I'd like to smoothly "animate" the google map marker for each vehicle by setting its position along an interpolated path between its last X/Y point and the current one. I call the URL to get a JSON object with all the current vehicle positions every 15 sec via a setInterval call. Inside that I iterate over each vehicle in the JSON object and set the vehicle position. I have functions to animate the motion but it only works reliably for one vehicle, I believe because my nested setInterval function will not complete before the next step in the for loop it's enclosed in. Is there anyway to have the inner setInterval function run to completion before the next "i" in my for loop?
setInterval(function() {
$(document).ready(function() {
$.getJSON("http://localhost:8080/portal/frfeed/query/tampa_sw/paraVehicle?r=" + Math.random(),function(vehicles){
$.each(vehicles, function(index, d){
if(d.heading>=0 && d.heading<22.5) direction="NORTH";
else if(d.heading>=22.5 && d.heading<67.5) direction="NORTHEAST";
else if(d.heading>=67.5 && d.heading<112.5) direction="EAST";
else if(d.heading>=112.5 && d.heading<157.5) direction="SOUTHEAST";
else if(d.heading>=157.5 && d.heading<202.5) direction="SOUTH";
else if(d.heading>=202.5 && d.heading<247.5) direction="SOUTHWEST";
else if(d.heading>=247.5 && d.heading<292.5) direction="WEST";
else if(d.heading>=292.5 && d.heading<338) direction="NORTHWEST";
else direction="NORTH";
vehicle = "";
for (var i=0; i<vMarkers.length; i++) {
if( vMarkers[i][0] === d.internalVehicleId ) {
var path;
var latlng = new google.maps.LatLng(d.latitude,d.longitude);
vMarkers[i][2] = vMarkers[i][1].getPosition().lat();
vMarkers[i][3] = vMarkers[i][1].getPosition().lng();
vMarkers[i][4] = latlng;
vMarkers[i][1].setTitle('Vehicle: ' + d.internalVehicleId + '\r\n' + 'Last Update: ' + d.time + '\r\n' + 'Traveling: ' + direction + ' # ' + d.speed + ' mph');
path = vPolys[i][1].getPath();
path.push(latlng);
vPolys[i][1].setPath(path);
vehicle = vMarkers[i][0];
var lat = vMarkers[i][2];
var lng = vMarkers[i][3];
var latlngTo = vMarkers[i][4];
var latLngFrom = new google.maps.LatLng(lat,lng);
j = 0;
// function below only works correctly if filtered for one vehicle as below, otherwise, all
// markers randomly move and don't stop due to the setInterval being called inside the for loop
if (distance(latlngTo.lat(), latlngTo.lng(),latLngFrom.lat(), latLngFrom.lng()) > 20 && vMarkers[i][0] == "1329") {
iv = window.setInterval(function() {
j++;
var pos = mercatorInterpolate(map, latLngFrom, latlngTo, j/50);
vMarkers[i][1].setPosition(pos);
if (j >= 50) {
window.clearInterval(iv);
}
}, 20);
}
else {
vMarkers[i][1].setPosition(latlngTo);
};
break;
}
}
if( vehicle == "") {
color = get_random_color();
marker = new StyledMarker({
styleIcon:new StyledIcon(StyledIconTypes.BUBBLE,{color:color, fore: "ffffff",text: d.internalVehicleId}),
position: new google.maps.LatLng(d.latitude,d.longitude),
title: 'Vehicle: ' + d.internalVehicleId + '\r\n' + 'Last Update: ' + d.time + '\r\n' + 'Traveling: ' + direction + ' # ' + d.speed + ' mph',
map: map
});
var polyOptions = {
strokeColor: color,
strokeOpacity: 1.0,
map: map,
strokeWeight: 3
};
poly = new google.maps.Polyline(polyOptions);
var latlng = new google.maps.LatLng(d.latitude,d.longitude);
vMarkers.push([d.internalVehicleId, marker, d.latitude, d.longitude, latlng]);
var path = poly.getPath();
path.push(latlng);
poly.setPath(path);
vPolys.push([d.internalVehicleId, poly])
vehicle = "";
}
});//$.each(vehicles, function(index, d){
function mercatorInterpolate(map, latLngFrom, latLngTo, fraction) {
// Get projected points
var projection = map.getProjection();
var pointFrom = projection.fromLatLngToPoint(latLngFrom);
var pointTo = projection.fromLatLngToPoint(latLngTo);
// Adjust for lines that cross the 180 meridian
if (Math.abs(pointTo.x - pointFrom.x) > 128) {
if (pointTo.x > pointFrom.x)
pointTo.x -= 256;
else
pointTo.x += 256;
}
// Calculate point between
var x = pointFrom.x + (pointTo.x - pointFrom.x) * fraction;
var y = pointFrom.y + (pointTo.y - pointFrom.y) * fraction;
var pointBetween = new google.maps.Point(x, y);
// Project back to lat/lng
var latLngBetween = projection.fromPointToLatLng(pointBetween);
return latLngBetween;
}
function distance(lat1,lon1,lat2,lon2) {
var R = 6371;
var dLat = (lat2-lat1) * Math.PI / 180;
var dLon = (lon2-lon1) * Math.PI / 180;
var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
Math.cos(lat1 * Math.PI / 180 ) * Math.cos(lat2 * 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;
return Math.abs(d*1000);
}
}); //$.getJSON(...., function(vehicles) {
}); //$(document).ready(function() {
}, 16000); // setInterval(function(){

No, setInterval is Asynchronous. You have to program in a way that works with asycronous code, rather then trying to force it to be synchronous.
For animation you should really be using requestAnimationFrame to get smooth results.
I would create a frames array, pushing an array of the cars every 15 seconds. Each car storing it's position
var frames = [[{x: 10, y:2},{x: 5, y:6}], [{x: 12, y:4},{x: 7, y:8}]]
I would then use requestAnimationFrame and interpolate the current position of each car
var currentFrame = 0;
var startTime = 0;
function update(){
var currentTime = newDate();
startTime || startTime = currentTime;
var elaspedTime = Math.floor(currentTime.getTime() - startTime.getTime())/1000;
// increment the current frame if 15 seconds have elapsed
elaspedTime%15 === 0 && currentFrame++;
// Get the current frame
var frame = frames[currentFrame],
nextFrame = frames[++currentFrame];
// Loop over each car in the frame
for(var i = 0; i < frame.length; i++){
// Calculate the difference in location
var xDiff = nextFrame[i].x - frame[i].x;
var yDiff = nextFrame[i].y - frame[i].y;
// interpolate the current position of the cars
var xPos = xDiff / elaspedTime%15;
var yPos = yDiff / elaspedTime%15;
// do some work here to set the position of the cars
}
requestAnimationFrame(update);
}
requestAnimationFrame(update);
You could optimize this much better then what I've done, but this is how I'd approach it.

Instead of trying to run multiple setInterval(), run just one, and iterate over all your vehicles within that one function call.
For example:
iv = setInterval(function() {
for (int i=0; i<vehicleArray.length;i++) {
// Do stuff for each vehicle.
}
}, 40);
Note that setInterval() doesn't guarantee the frequency at which it will be called, just the minumum interval. This can lead to haphazard tracking. Avoid this by reading the clock every time you enter the setInterval() function, and calculating new positions based on that.
Your code is trying to achieve 50 frames per second, which might prove to be optimistic. You can get a smooth effect at half that. i.e. at 40ms intervals.

How to add markers on Google Maps polylines based on distance along the line?

I am trying to create a Google Map where the user can plot the route he walked/ran/bicycled and see how long he ran. The GPolyline class with it’s getLength() method is very helpful in this regard (at least for Google Maps API V2), but I wanted to add markers based on distance, for example a marker for 1 km, 5 km, 10 km, etc., but it seems that there is no obvious way to find a point on a polyline based on how far along the line it is. Any suggestions?

Having answered a similar problem a couple of months ago on how to tackle this on the server-side in SQL Server 2008, I am porting the same algorithm to JavaScript using the Google Maps API v2.
For the sake of this example, let's use a simple 4-point polyline, with a total length of circa 8,800 meters. The snippet below will define this polyline and will render it on the map:
var map = new GMap2(document.getElementById('map_canvas'));
var points = [
new GLatLng(47.656, -122.360),
new GLatLng(47.656, -122.343),
new GLatLng(47.690, -122.310),
new GLatLng(47.690, -122.270)
];
var polyline = new GPolyline(points, '#f00', 6);
map.setCenter(new GLatLng(47.676, -122.343), 12);
map.addOverlay(polyline);
Now before we approach the actual algorithm, we will need a function that returns the destination point when given a start point, an end point, and the distance to travel along that line, Luckily, there are a few handy JavaScript implementations by Chris Veness at Calculate distance, bearing and more between Latitude/Longitude points.
In particular I have adapted the following two methods from the above source to work with Google's GLatLng class:
Destination point given distance and bearing from start point
Bearing
These were used to extend Google's GLatLng class with a method moveTowards(), which when given another point and a distance in meters, it will return another GLatLng along that line when the distance is travelled from the original point towards the point passed as a parameter.
GLatLng.prototype.moveTowards = function(point, distance) {
var lat1 = this.lat().toRad();
var lon1 = this.lng().toRad();
var lat2 = point.lat().toRad();
var lon2 = point.lng().toRad();
var dLon = (point.lng() - this.lng()).toRad();
// Find the bearing from this point to the next.
var brng = Math.atan2(Math.sin(dLon) * Math.cos(lat2),
Math.cos(lat1) * Math.sin(lat2) -
Math.sin(lat1) * Math.cos(lat2) *
Math.cos(dLon));
var angDist = distance / 6371000; // Earth's radius.
// Calculate the destination point, given the source and bearing.
lat2 = Math.asin(Math.sin(lat1) * Math.cos(angDist) +
Math.cos(lat1) * Math.sin(angDist) *
Math.cos(brng));
lon2 = lon1 + Math.atan2(Math.sin(brng) * Math.sin(angDist) *
Math.cos(lat1),
Math.cos(angDist) - Math.sin(lat1) *
Math.sin(lat2));
if (isNaN(lat2) || isNaN(lon2)) return null;
return new GLatLng(lat2.toDeg(), lon2.toDeg());
}
Having this method, we can now tackle the problem as follows:
Iterate through each point of the path.
Find the distance between the current point in the iteration to the next point.
If the distance in point 2 is greater the distance we need to travel on the path:
...then the destination point is between this point and the next. Simply apply the moveTowards() method to the current point, passing the next point and the distance to travel. Return the result and break the iteration.
Else:
...the destination point is further in the path from the next point in the iteration. We need to subtract the distance between this point and the next point from the total distance to travel along the path. Continue through the iteration with the modified distance.
You may have noticed that we can easily implement the above recursively, instead of iteratively. So let's do it:
function moveAlongPath(points, distance, index) {
index = index || 0; // Set index to 0 by default.
if (index < points.length) {
// There is still at least one point further from this point.
// Construct a GPolyline to use its getLength() method.
var polyline = new GPolyline([points[index], points[index + 1]]);
// Get the distance from this point to the next point in the polyline.
var distanceToNextPoint = polyline.getLength();
if (distance <= distanceToNextPoint) {
// distanceToNextPoint is within this point and the next.
// Return the destination point with moveTowards().
return points[index].moveTowards(points[index + 1], distance);
}
else {
// The destination is further from the next point. Subtract
// distanceToNextPoint from distance and continue recursively.
return moveAlongPath(points,
distance - distanceToNextPoint,
index + 1);
}
}
else {
// There are no further points. The distance exceeds the length
// of the full path. Return null.
return null;
}
}
With the above method, if we define an array of GLatLng points, and we invoke our moveAlongPath() function with this array of points and with a distance of 2,500 meters, it will return a GLatLng on that path at 2.5km from the first point.
var points = [
new GLatLng(47.656, -122.360),
new GLatLng(47.656, -122.343),
new GLatLng(47.690, -122.310),
new GLatLng(47.690, -122.270)
];
var destinationPointOnPath = moveAlongPath(points, 2500);
// destinationPointOnPath will be a GLatLng on the path
// at 2.5km from the start.
Therefore all we need to do is to call moveAlongPath() for each check point we need on the path. If you need three markers at 1km, 5km and 10km, you can simply do:
map.addOverlay(new GMarker(moveAlongPath(points, 1000)));
map.addOverlay(new GMarker(moveAlongPath(points, 5000)));
map.addOverlay(new GMarker(moveAlongPath(points, 10000)));
Note however that moveAlongPath() may return null if we request a check point further from the total length of the path, so it will be wiser to check for the return value before passing it to new GMarker().
We can put this together for the full implementation. In this example we are dropping a marker every 1,000 meters along the 8.8km path defined earlier:
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8"/>
<title>Google Maps - Moving point along a path</title>
<script src="http://maps.google.com/maps?file=api&v=2&sensor=false"
type="text/javascript"></script>
</head>
<body onunload="GUnload()">
<div id="map_canvas" style="width: 500px; height: 300px;"></div>
<script type="text/javascript">
Number.prototype.toRad = function() {
return this * Math.PI / 180;
}
Number.prototype.toDeg = function() {
return this * 180 / Math.PI;
}
GLatLng.prototype.moveTowards = function(point, distance) {
var lat1 = this.lat().toRad();
var lon1 = this.lng().toRad();
var lat2 = point.lat().toRad();
var lon2 = point.lng().toRad();
var dLon = (point.lng() - this.lng()).toRad();
// Find the bearing from this point to the next.
var brng = Math.atan2(Math.sin(dLon) * Math.cos(lat2),
Math.cos(lat1) * Math.sin(lat2) -
Math.sin(lat1) * Math.cos(lat2) *
Math.cos(dLon));
var angDist = distance / 6371000; // Earth's radius.
// Calculate the destination point, given the source and bearing.
lat2 = Math.asin(Math.sin(lat1) * Math.cos(angDist) +
Math.cos(lat1) * Math.sin(angDist) *
Math.cos(brng));
lon2 = lon1 + Math.atan2(Math.sin(brng) * Math.sin(angDist) *
Math.cos(lat1),
Math.cos(angDist) - Math.sin(lat1) *
Math.sin(lat2));
if (isNaN(lat2) || isNaN(lon2)) return null;
return new GLatLng(lat2.toDeg(), lon2.toDeg());
}
function moveAlongPath(points, distance, index) {
index = index || 0; // Set index to 0 by default.
if (index < points.length) {
// There is still at least one point further from this point.
// Construct a GPolyline to use the getLength() method.
var polyline = new GPolyline([points[index], points[index + 1]]);
// Get the distance from this point to the next point in the polyline.
var distanceToNextPoint = polyline.getLength();
if (distance <= distanceToNextPoint) {
// distanceToNextPoint is within this point and the next.
// Return the destination point with moveTowards().
return points[index].moveTowards(points[index + 1], distance);
}
else {
// The destination is further from the next point. Subtract
// distanceToNextPoint from distance and continue recursively.
return moveAlongPath(points,
distance - distanceToNextPoint,
index + 1);
}
}
else {
// There are no further points. The distance exceeds the length
// of the full path. Return null.
return null;
}
}
var map = new GMap2(document.getElementById('map_canvas'));
var points = [
new GLatLng(47.656, -122.360),
new GLatLng(47.656, -122.343),
new GLatLng(47.690, -122.310),
new GLatLng(47.690, -122.270)
];
var polyline = new GPolyline(points, '#f00', 6);
var nextMarkerAt = 0; // Counter for the marker checkpoints.
var nextPoint = null; // The point where to place the next marker.
map.setCenter(new GLatLng(47.676, -122.343), 12);
// Draw the path on the map.
map.addOverlay(polyline);
// Draw the checkpoint markers every 1000 meters.
while (true) {
// Call moveAlongPath which will return the GLatLng with the next
// marker on the path.
nextPoint = moveAlongPath(points, nextMarkerAt);
if (nextPoint) {
// Draw the marker on the map.
map.addOverlay(new GMarker(nextPoint));
// Add +1000 meters for the next checkpoint.
nextMarkerAt += 1000;
}
else {
// moveAlongPath returned null, so there are no more check points.
break;
}
}
</script>
</body>
</html>
Screenshot of the above example, showing a marker every 1,000 meters:

These are the prototypes for the required functions:
google.maps.Polygon.prototype.Distance = function() {
var dist = 0;
for (var i=1; i < this.getPath().getLength(); i++) {
dist += this.getPath().getAt(i).distanceFrom(this.getPath().getAt(i-1));
}
return dist;
}
google.maps.LatLng.prototype.distanceFrom = function(newLatLng) {
//var R = 6371; // km (change this constant to get miles)
var R = 6378100; // meters
var lat1 = this.lat();
var lon1 = this.lng();
var lat2 = newLatLng.lat();
var lon2 = newLatLng.lng();
var dLat = (lat2-lat1) * Math.PI / 180;
var dLon = (lon2-lon1) * Math.PI / 180;
var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
Math.cos(lat1 * Math.PI / 180 ) * Math.cos(lat2 * 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;
return d;
}
source

Possibly the best approach would be to calculate where these points are.
As a basic algorithm you could iterate over all the points in the Polyline, and calculate the cumulative distance - if the next segment puts you over your distance, you can interpolate the point where the distance has been reached - then simply add a point of interest to your map for that.

I have used Martin Zeitler method to work with Google Map V3 and its working fine.
function init() {
var mapOptions = {
zoom: 15,
center: new google.maps.LatLng(-6.208437004433984, 106.84543132781982),
suppressInfoWindows: true,
};
// Get all html elements for map
var mapElement = document.getElementById('map1');
// Create the Google Map using elements
map = new google.maps.Map(mapElement, mapOptions);
var nextMarkerAt = 0; // Counter for the marker checkpoints.
var nextPoint = null; // The point where to place the next marker.
while (true) {
var routePoints = [ new google.maps.LatLng(47.656, -122.360),
new google.maps.LatLng(47.656, -122.343),
new google.maps.LatLng(47.690, -122.310),
new google.maps.LatLng(47.690, -122.270)];
nextPoint = moveAlongPath(routePoints, nextMarkerAt);
if (nextPoint) {
//Adding marker from localhost
MarkerIcon = "http://192.168.1.1/star.png";
var marker = new google.maps.Marker
({position: nextPoint,
map: map,
icon: MarkerIcon
});
// Add +1000 meters for the next checkpoint.
nextMarkerAt +=1000;
}
else {
// moveAlongPath returned null, so there are no more check points.
break;
}
}
}
Number.prototype.toRad = function () {
return this * Math.PI / 180;
}
Number.prototype.toDeg = function () {
return this * 180 / Math.PI;
}
function moveAlongPath(point, distance, index) {
index = index || 0; // Set index to 0 by default.
var routePoints = [];
for (var i = 0; i < point.length; i++) {
routePoints.push(point[i]);
}
if (index < routePoints.length) {
// There is still at least one point further from this point.
// Construct a GPolyline to use the getLength() method.
var polyline = new google.maps.Polyline({
path: [routePoints[index], routePoints[index + 1]],
strokeColor: '#FF0000',
strokeOpacity: 0.8,
strokeWeight: 2,
fillColor: '#FF0000',
fillOpacity: 0.35
});
// Get the distance from this point to the next point in the polyline.
var distanceToNextPoint = polyline.Distance();
if (distance <= distanceToNextPoint) {
// distanceToNextPoint is within this point and the next.
// Return the destination point with moveTowards().
return moveTowards(routePoints, distance,index);
}
else {
// The destination is further from the next point. Subtract
// distanceToNextPoint from distance and continue recursively.
return moveAlongPath(routePoints,
distance - distanceToNextPoint,
index + 1);
}
}
else {
// There are no further points. The distance exceeds the length
// of the full path. Return null.
return null;
}
}
function moveTowards(point, distance,index) {
var lat1 = point[index].lat.toRad();
var lon1 = point[index].lng.toRad();
var lat2 = point[index+1].lat.toRad();
var lon2 = point[index+1].lng.toRad();
var dLon = (point[index + 1].lng - point[index].lng).toRad();
// Find the bearing from this point to the next.
var brng = Math.atan2(Math.sin(dLon) * Math.cos(lat2),
Math.cos(lat1) * Math.sin(lat2) -
Math.sin(lat1) * Math.cos(lat2) *
Math.cos(dLon));
var angDist = distance / 6371000; // Earth's radius.
// Calculate the destination point, given the source and bearing.
lat2 = Math.asin(Math.sin(lat1) * Math.cos(angDist) +
Math.cos(lat1) * Math.sin(angDist) *
Math.cos(brng));
lon2 = lon1 + Math.atan2(Math.sin(brng) * Math.sin(angDist) *
Math.cos(lat1),
Math.cos(angDist) - Math.sin(lat1) *
Math.sin(lat2));
if (isNaN(lat2) || isNaN(lon2)) return null;
return new google.maps.LatLng(lat2.toDeg(), lon2.toDeg());
}
google.maps.Polyline.prototype.Distance = function () {
var dist = 0;
for (var i = 1; i < this.getPath().getLength(); i++) {
dist += this.getPath().getAt(i).distanceFrom(this.getPath().getAt(i - 1));
}
return dist;
}
google.maps.LatLng.prototype.distanceFrom = function (newLatLng) {
//var R = 6371; // km (change this constant to get miles)
var R = 6378100; // meters
var lat1 = this.lat();
var lon1 = this.lng();
var lat2 = newLatLng.lat();
var lon2 = newLatLng.lng();
var dLat = (lat2 - lat1) * Math.PI / 180;
var dLon = (lon2 - lon1) * Math.PI / 180;
var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
Math.cos(lat1 * Math.PI / 180) * Math.cos(lat2 * 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;
return d;
}

I wanted to port Daniel Vassalo's answer to iOS, but it wasn't worked properly and some markers were misplaced until I changed
var dLon = (point.lng() - this.lng()).toRad();
to
var dLon = point.lng().toRad() - this.lng().toRad();
So if anyone having a trouble to figure out why are the markers are misplaced, try this and maybe it will help.