Mercator projection

mercator_projection.js

// https://en.wikipedia.org/wiki/Mercator_projection
function MercatorProjection(){
    this.EARTH_RADIUS = 6378137 // WGS-84
    this.EARTH_HALF_CIRCUMFERENCE = Math.PI * this.EARTH_RADIUS // 20037508.342789244
    this.EARTH_METERS_PER_DEGREE = (Math.PI * this.EARTH_RADIUS) / 180   // 111319.49079327358
    this.RADIAN = Math.PI / 180
    this.DEGREE = 180 / Math.PI
}

MercatorProjection.prototype.toDegree = function(radian){
    return this.DEGREE * radian
}

MercatorProjection.prototype.toRadian = function(degree){
    return this.RADIAN * degree
}

MercatorProjection.prototype.LatLonToMeters = function(lat, lon){
    // for radians
    //mx = this.toRadian(EARTH_RADIUS * lon)
    //my = EARTH_RADIUS * Math.log( Math.tan(Math.PI / 4.0 + (lat*this.RADIAN) / 2.0))
    // for degrees
    var mx = this.EARTH_METERS_PER_DEGREE * lon
    var my = this.EARTH_RADIUS * Math.log(Math.tan(this.toRadian(45 + lat / 2.0)))
    return [mx, my]
}

MercatorProjection.prototype.MetersToLatLon = function(mx, my){
    // for degrees
    var lon = mx / this.EARTH_METERS_PER_DEGREE
    //lat = this.DEGREE * (2.0 * Math.atan(Math.exp((my/this.EARTH_METERS_PER_DEGREE)*this.RADIAN)) - Math.PI / 2.0)
    // for radians
    //lon = (mx / this.EARTH_RADIUS) * this.DEGREE
    var lat = this.toDegree(2.0 * Math.atan(Math.exp(my/this.EARTH_RADIUS)) - Math.PI / 2.0)
    return [lat, lon]
}

MercatorProjection.prototype.MoveTo = function(lat, lon, distance, heading){
    var heading_rad = this.toRadian(heading)
    var [mx, my] = this.LatLonToMeters(lat, lon)
    var scale_factor = Math.cos(this.toRadian(lat))
    var map_distance = scale_factor * distance
    mx = mx + map_distance * Math.sin(heading_rad)
    my = my + map_distance * Math.cos(heading_rad)
    return this.MetersToLatLon(mx, my)
}