PowerPan/leaflet.nauticscale

L.Control.ScaleNautic = L.Control.Scale.extend({
    options: {
        nautic: false
    },

    _addScales: function(options, className, container) {
        L.Control.Scale.prototype._addScales.call(this, options, className, container);
        L.setOptions(options);
        if (this.options.nautic) {
            this._nScale = L.DomUtil.create('div', className, container);
        }
    },

    _updateScales: function (maxMeters) {
        L.Control.Scale.prototype._updateScales.call(this, maxMeters);
        if (this.options.nautic && maxMeters) {
            this._updateNautic(maxMeters);
        }
    },

    _updateNautic: function (maxMeters) {
        var scale = this._nScale,
            maxNauticalMiles = maxMeters / 1852, nauticalMiles;

        nauticalMiles = this._getRoundNum(maxNauticalMiles);

        scale.style.width = Math.round(this.options.maxWidth * (nauticalMiles / maxNauticalMiles)) - 10 + 'px';
        scale.innerHTML = nauticalMiles + ' nm';
    },
    
    _getRoundNum: function (num) {
        var pow10, d;
        if (num >= 1) {
            pow10 = Math.pow(10, (Math.floor(num) + '').length - 1);
            d = num / pow10;
        }
        else {
            pow10 = 1;
            d = num;
            while (d < 1) {
                d *= 10;
                pow10 *= 10;
            }
        } 
        
        d = d >= 10 ? 10 :
            d >= 5 ? 5 :
            d >= 3 ? 3 :
            d >= 2 ? 2 : 1;
        
        return num >= 1 ? pow10 * d : d / pow10;
    }
});

L.control.scalenautic = function (options) {
    return new L.Control.ScaleNautic(options);
};