Se hai bisogno di una soluzione JavaScript, considera questi functionse questo violino :
var gis = {
/**
* All coordinates expected EPSG:4326
* @param {Array} start Expected [lon, lat]
* @param {Array} end Expected [lon, lat]
* @return {number} Distance - meter.
*/
calculateDistance: function(start, end) {
var lat1 = parseFloat(start[1]),
lon1 = parseFloat(start[0]),
lat2 = parseFloat(end[1]),
lon2 = parseFloat(end[0]);
return gis.sphericalCosinus(lat1, lon1, lat2, lon2);
},
/**
* All coordinates expected EPSG:4326
* @param {number} lat1 Start Latitude
* @param {number} lon1 Start Longitude
* @param {number} lat2 End Latitude
* @param {number} lon2 End Longitude
* @return {number} Distance - meters.
*/
sphericalCosinus: function(lat1, lon1, lat2, lon2) {
var radius = 6371e3; // meters
var dLon = gis.toRad(lon2 - lon1),
lat1 = gis.toRad(lat1),
lat2 = gis.toRad(lat2),
distance = Math.acos(Math.sin(lat1) * Math.sin(lat2) +
Math.cos(lat1) * Math.cos(lat2) * Math.cos(dLon)) * radius;
return distance;
},
/**
* @param {Array} coord Expected [lon, lat] EPSG:4326
* @param {number} bearing Bearing in degrees
* @param {number} distance Distance in meters
* @return {Array} Lon-lat coordinate.
*/
createCoord: function(coord, bearing, distance) {
/** http://www.movable-type.co.uk/scripts/latlong.html
* φ is latitude, λ is longitude,
* θ is the bearing (clockwise from north),
* δ is the angular distance d/R;
* d being the distance travelled, R the earth’s radius*
**/
var
radius = 6371e3, // meters
δ = Number(distance) / radius, // angular distance in radians
θ = gis.toRad(Number(bearing));
φ1 = gis.toRad(coord[1]),
λ1 = gis.toRad(coord[0]);
var φ2 = Math.asin(Math.sin(φ1)*Math.cos(δ) +
Math.cos(φ1)*Math.sin(δ)*Math.cos(θ));
var λ2 = λ1 + Math.atan2(Math.sin(θ) * Math.sin(δ)*Math.cos(φ1),
Math.cos(δ)-Math.sin(φ1)*Math.sin(φ2));
// normalise to -180..+180°
λ2 = (λ2 + 3 * Math.PI) % (2 * Math.PI) - Math.PI;
return [gis.toDeg(λ2), gis.toDeg(φ2)];
},
/**
* All coordinates expected EPSG:4326
* @param {Array} start Expected [lon, lat]
* @param {Array} end Expected [lon, lat]
* @return {number} Bearing in degrees.
*/
getBearing: function(start, end){
var
startLat = gis.toRad(start[1]),
startLong = gis.toRad(start[0]),
endLat = gis.toRad(end[1]),
endLong = gis.toRad(end[0]),
dLong = endLong - startLong;
var dPhi = Math.log(Math.tan(endLat/2.0 + Math.PI/4.0) /
Math.tan(startLat/2.0 + Math.PI/4.0));
if (Math.abs(dLong) > Math.PI) {
dLong = (dLong > 0.0) ? -(2.0 * Math.PI - dLong) : (2.0 * Math.PI + dLong);
}
return (gis.toDeg(Math.atan2(dLong, dPhi)) + 360.0) % 360.0;
},
toDeg: function(n) { return n * 180 / Math.PI; },
toRad: function(n) { return n * Math.PI / 180; }
};
Quindi, se vuoi calcolare una nuova coordinata, può essere così:
var start = [15, 38.70250];
var end = [21.54967, 38.70250];
var total_distance = gis.calculateDistance(start, end); // meters
var percent = 10;
// this can be also meters
var distance = (percent / 100) * total_distance;
var bearing = gis.getBearing(start, end);
var new_coord = gis.createCoord(icon_coord, bearing, distance);