Lock Orientation When Using OpenLayers Geolocation - geolocation

Question

We use an embedded map to track our location while driving in the field. Currently the map rotates to match the GPS's orientation. We've found that to be very disorienting and I'd like to lock the orientation North (0 degrees). I still would like the map to track location and indicate heading if available. Below is the snipped from the map's javascript file pertaining to geolocation.
map.addLayer(addressLayer);
// Geolocation marker
var markerEl = document.getElementById('geolocation_marker');
var marker = new ol.Overlay({
positioning: 'center-center',
element: markerEl,
stopEvent: false
});
map.addOverlay(marker);
// LineString to store the different geolocation positions. This LineString
// is time aware.
// The Z dimension is actually used to store the rotation (heading).
var positions = new ol.geom.LineString([],
/** #type {ol.geom.GeometryLayout} */ ('XYZM'));
// Geolocation Control
var geolocation = new ol.Geolocation(/** #type {olx.GeolocationOptions} */ ({
projection: view.getProjection(),
tracking: true,
trackingOptions: {
maximumAge: 10000,
enableHighAccuracy: true,
timeout: 600000
}
}));
var deltaMean = 500; // the geolocation sampling period mean in ms
// Listen to position changes
geolocation.on('change', function(evt) {
var position = geolocation.getPosition();
var accuracy = geolocation.getAccuracy();
var heading = geolocation.getHeading() || 0;
var speed = geolocation.getSpeed() || 0;
var m = Date.now();
addPosition(position, heading, m, speed);
map.getView().setCenter(geolocation.getPosition());
document.getElementById("locate").style.backgroundColor = 'rgba(0,128,0,1)';
locateUser = true;
});
geolocation.on('error', function(error) {
var errors = {
1: 'Permission denied to locate device',
2: 'Position unavailable',
3: 'Request timeout'
};
if (error.code){
document.getElementById("locate").style.backgroundColor = 'rgba(255,0,0,1)';
locateUser = false;
}
alert("Error: " + errors[error.code]);
});
// convert radians to degrees
function radToDeg(rad) {
return rad * 360 / (Math.PI * 2);
}
// convert degrees to radians
function degToRad(deg) {
return deg * Math.PI * 2 / 360;
}
// modulo for negative values
function mod(n) {
return ((n % (2 * Math.PI)) + (2 * Math.PI)) % (2 * Math.PI);
}
function addPosition(position, heading, m, speed) {
var x = position[0];
var y = position[1];
var fCoords = positions.getCoordinates();
var previous = fCoords[fCoords.length - 1];
var prevHeading = previous && previous[2];
if (prevHeading) {
var headingDiff = heading - mod(prevHeading);
// force the rotation change to be less than 180°
if (Math.abs(headingDiff) > Math.PI) {
var sign = (headingDiff >= 0) ? 1 : -1;
headingDiff = - sign * (2 * Math.PI - Math.abs(headingDiff));
}
heading = prevHeading + headingDiff;
}
positions.appendCoordinate([x, y, heading, m]);
// only keep the 20 last coordinates
positions.setCoordinates(positions.getCoordinates().slice(-20));
// FIXME use speed instead
if (heading && speed) {
markerEl.src = 'images/geolocation_marker_heading.png';
} else {
markerEl.src = 'images/geolocation_marker.png';
}
}
var previousM = 0;
// change center and rotation before render
map.beforeRender(function(map, frameState) {
if (frameState !== null) {
// use sampling period to get a smooth transition
var m = frameState.time - deltaMean * 1.5;
m = Math.max(m, previousM);
previousM = m;
// interpolate position along positions LineString
var c = positions.getCoordinateAtM(m, true);
var view = frameState.viewState;
if (c) {
view.rotation = -c[2];
marker.setPosition(c);
}
}
return true; // Force animation to continue
});
// postcompose callback
function render() {
map.render();
}
// geolocate device
var geolocateBtn = document.getElementById('locate');
geolocateBtn.addEventListener('click', function() {
if(locateUser){
geolocation.setTracking(false);
geolocateBtn.style.backgroundColor = 'rgba(255,0,0,1)';
locateUser = false;
}
else{
geolocation.setTracking(true);
map.getView().setCenter(geolocation.getPosition());
geolocateBtn.style.backgroundColor = 'rgba(0,128,0,1)';
map.on('postcompose', render);
map.render();
locateUser = true;
}
}, false);
addLocations(QueryString);
function addLocations(addressArr) {
if (nextAddress < addressArr.length) {
setTimeout(function(){
if (addressArr[nextAddress] !== undefined){
geocodeAddress(addressArr[nextAddress]);
}
}, delay);
}
if(nextAddress == addressArr.length) {
view.fitExtent(vectorSource.getExtent(), map.getSize());
}
}
function geocodeAddress (location) {
$.getJSON('http://maps.googleapis.com/maps/api/geocode/json?address='+location.address+'&sensor=false', null, function (data) {
if(data.status === 'OK'){
var p = data.results[0].geometry.location;
var color = location.status == 'incomplete' ? 'red' : 'green';
var pointFeature = new ol.Feature({
geometry: new ol.geom.Point(ol.proj.transform([p.lng, p.lat], 'EPSG:4326',
'EPSG:3857')),
fillColor: color,
id: location.id
});
vectorSource.addFeature(pointFeature);
addresses.push(pointFeature);
nextAddress+=1;
addLocations(QueryString);
}
if(data.status === 'OVER_QUERY_LIMIT'){
delay += delay;
}
});
}

Answer 1

Here is the relevant ol3 code that's causing the rotation to happen.
By setting view.rotation = 0; you may resolve the issue.