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I've been struggling with this for a while & need some advice. I have seen some similar topics but can't find an answer that works for me.
I am creating an app using google maps API that will determine your location, determine a specific point (point b) and then move an arrow to point in the direction of point b. I am having trouble calculating the bearing, could anyone offer some assistance?
I have: - the lat/lng of point a - the lat/lng of point b - the device knows where North is and I am able to calculate how many degrees away from north the device is pointing
I need: a calculation that will take this information and spit out a number of degrees to point the arrow.
I have looked here which seems useful but I still can't get it working - it's returning NaN
http://www.movable-type.co.uk/scripts/latlong.html
I'm not really a js pro so would really appreciate some guidance here.
Thanks very much!
877
You can use the Geometry Library.
You need to add it to the API call:
https://maps.googleapis.com/maps/api/js?libraries=geometry
Then use the computeHeading method:
var heading = google.maps.geometry.spherical.computeHeading(pointA, pointB);
where pointA and pointB are the two LatLng objects.
https://developers.google.com/maps/documentation/javascript/reference?csw=1#spherical
104
Below is a dynamically working example.
<!DOCTYPE html>
<html>
<head>
<style>
html,
body,
#map-canvas {
height: 100%;
width: 100%;
margin: 0px;
padding: 0px;
}
</style>
</head>
<body>
<script src="https://maps.googleapis.com/maps/api/js?sensor=false&libraries=geometry&ext=.js"></script>
<div id="info"></div>
<div id="map-canvas"></div>
<script type="text/javascript">
var map;
var infowindow = new google.maps.InfoWindow();
function initialize() {
geocoder = new google.maps.Geocoder();
var latlng = new google.maps.LatLng(32.0748, 34.774);
var mapOptions = {
zoom: 15,
center: latlng
}
map = new google.maps.Map(document.getElementById('map-canvas'), mapOptions);
point1 = new google.maps.Marker({
map: map,
draggable: true,
position: google.maps.geometry.spherical.computeOffset(map.getCenter(), 0, 80)
});
google.maps.event.addListener(point1, 'dragend', bisectAngle);
point2 = new google.maps.Marker({
map: map,
draggable: true,
position: google.maps.geometry.spherical.computeOffset(map.getCenter(), 800, -58.6)
});
google.maps.event.addListener(point2, 'dragend', bisectAngle);
var poly3 = new google.maps.Polyline({
path: [point1.getPosition(), point2.getPosition()],
map: map
});
poly3.binder = new MVCArrayBinder(poly3.getPath());
point1.bindTo('position', poly3.binder, '0'); //this makes the line bind to point 1
point2.bindTo('position', poly3.binder, '1'); //and point 2
var bounds = new google.maps.LatLngBounds();
bounds.extend(point1);
bounds.extend(point2);
map.fitBounds(bounds); //zooms in
}
google.maps.event.addDomListener(window, 'load', initialize);
google.maps.event.addDomListener(window, 'load', bisectAngle);
function bisectAngle() {
var head1 = google.maps.geometry.spherical.computeHeading(point1.getPosition(), point2.getPosition());
document.getElementById('info').innerHTML = "Bearing is " + head1.toFixed(1) + " or " + (head1 + 90).toFixed(1) + " if E-W is 0. Better try daniel street...";
}
/*
* Use bindTo to allow dynamic drag of markers to refresh poly.
*/
function MVCArrayBinder(mvcArray) { //credit to https://stackoverflow.com/a/26663570/2381899
this.array_ = mvcArray;
}
MVCArrayBinder.prototype = new google.maps.MVCObject();
MVCArrayBinder.prototype.get = function (key) {
if (!isNaN(parseInt(key))) {
return this.array_.getAt(parseInt(key));
} else {
this.array_.get(key);
}
}
MVCArrayBinder.prototype.set = function (key, val) {
if (!isNaN(parseInt(key))) {
this.array_.setAt(parseInt(key), val);
} else {
this.array_.set(key, val);
}
}
</script>
</body>
</html>
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