A function to calculate if a geo point is in a cirlce

isInArea.coffee

###*
 * Check if a given point in a circle
 * @param  {Object}  circle a cirle object with radius and center point
 * @param  {Object}  point  a point need to be checked
 * @return {Boolean}        True or False
###
Map.isInArea = (circle, point) ->
    getDistance = (lng1, lat1, lng2, lat2) ->
        # Radisu of the erath in km
        R = 6371
        dLat = (lat2 - lat1).toRad()
        dLng = (lng2 - lng1).toRad()
        a = Math.sin(dLat/2) * Math.sin(dLat/2) + Math.cos(lat1.toRad()) * Math.cos(lat2.toRad()) * Math.sin(dLng/2) * Math.sin(dLng/2)
        c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a))
        d = R * c
        return d

    # convert numeric degrees to radians
    if typeof Number.prototype.toRad is "undefined"
        Number.prototype.toRad = ->
            return this * Math.PI / 180

    # Convert unit
    # Unit 1 Km = 0.621371 Mile
    K2M = (k) ->
        UNIT = 0.621371
        return k * UNIT

    distance = K2M getDistance(circle.lng, circle.lat, point.lng, point.lat)

    return if distance > circle.radius then false else true