leaflet/src/control/Control.Scale.js

JavaScript library for mobile-friendly interactive maps

/*
 * L.Control.Scale is used for displaying metric/imperial scale on the map.
 */

L.Control.Scale = L.Control.extend({
	options: {
		position: 'bottomleft',
		maxWidth: 100,
		metric: true,
		imperial: true,
		updateWhenIdle: false
	},

	onAdd: function (map) {
		this._map = map;

		var className = 'leaflet-control-scale',
		    container = L.DomUtil.create('div', className),
		    options = this.options;

		this._addScales(options, className, container);

		map.on(options.updateWhenIdle ? 'moveend' : 'move', this._update, this);
		map.whenReady(this._update, this);

		return container;
	},

	onRemove: function (map) {
		map.off(this.options.updateWhenIdle ? 'moveend' : 'move', this._update, this);
	},

	_addScales: function (options, className, container) {
		if (options.metric) {
			this._mScale = L.DomUtil.create('div', className + '-line', container);
		}
		if (options.imperial) {
			this._iScale = L.DomUtil.create('div', className + '-line', container);
		}
	},

	_update: function () {
		var bounds = this._map.getBounds(),
		    centerLat = bounds.getCenter().lat,
		    halfWorldMeters = 6378137 * Math.PI * Math.cos(centerLat * Math.PI / 180),
		    dist = halfWorldMeters * (bounds.getNorthEast().lng - bounds.getSouthWest().lng) / 180,

		    size = this._map.getSize(),
		    options = this.options,
		    maxMeters = 0;

		if (size.x > 0) {
			maxMeters = dist * (options.maxWidth / size.x);
		}

		this._updateScales(options, maxMeters);
	},

	_updateScales: function (options, maxMeters) {
		if (options.metric && maxMeters) {
			this._updateMetric(maxMeters);
		}

		if (options.imperial && maxMeters) {
			this._updateImperial(maxMeters);
		}
	},

	_updateMetric: function (maxMeters) {
		var meters = this._getRoundNum(maxMeters);

		this._mScale.style.width = this._getScaleWidth(meters / maxMeters) + 'px';
		this._mScale.innerHTML = meters < 1000 ? meters + ' m' : (meters / 1000) + ' km';
	},

	_updateImperial: function (maxMeters) {
		var maxFeet = maxMeters * 3.2808399,
		    scale = this._iScale,
		    maxMiles, miles, feet;

		if (maxFeet > 5280) {
			maxMiles = maxFeet / 5280;
			miles = this._getRoundNum(maxMiles);

			scale.style.width = this._getScaleWidth(miles / maxMiles) + 'px';
			scale.innerHTML = miles + ' mi';

		} else {
			feet = this._getRoundNum(maxFeet);

			scale.style.width = this._getScaleWidth(feet / maxFeet) + 'px';
			scale.innerHTML = feet + ' ft';
		}
	},

	_getScaleWidth: function (ratio) {
		return Math.round(this.options.maxWidth * ratio) - 10;
	},

	_getRoundNum: function (num) {
		var pow10 = Math.pow(10, (Math.floor(num) + '').length - 1),
		    d = num / pow10;

		d = d >= 10 ? 10 : d >= 5 ? 5 : d >= 3 ? 3 : d >= 2 ? 2 : 1;

		return pow10 * d;
	}
});

L.control.scale = function (options) {
	return new L.Control.Scale(options);
};