Get Radius While Resizing Circle

Is it possible to get the radius of an existing circle while the circle is being resized? Google maps doesn't have a 'resizing' event and only triggers the radius_changed event aft

Solution 1:

There used to be an "article" in the Google Maps Javascript API v3 documentation that did this called "Fun with MVC".

This question on SO: How to style editable circle controls in Google Maps has an example from that article that outputs the radius as the circle is resized.

fiddle (from my answer to that question)

code snippet:

functioninit() {
        var mapDiv = document.getElementById('map-canvas');
        var map = new google.maps.Map(mapDiv, {
          center: new google.maps.LatLng(37.790234970864, -122.39031314844),
          zoom: 8,
          mapTypeId: google.maps.MapTypeId.ROADMAP
        });
        var distanceWidget = newDistanceWidget(map);
        google.maps.event.addListener(distanceWidget, 'distance_changed', function() {
          displayInfo(distanceWidget);
        });

        google.maps.event.addListener(distanceWidget, 'position_changed', function() {
          displayInfo(distanceWidget);
        });
      }

      google.maps.event.addDomListener(window, 'load', init);

      /** 
       * A distance widget that will display a circle that can be resized and will
       * provide the radius in km.
       *
       * @param {google.maps.Map} map The map on which to attach the distance widget.
       *
       * @constructor
       */functionDistanceWidget(map) {
        this.set('map', map);
        this.set('position', map.getCenter());

        var marker = new google.maps.Marker({
          draggable: true,
          icon: {
            url: "https://maps.gstatic.com/intl/en_us/mapfiles/markers2/measle_blue.png",
            size: new google.maps.Size(7, 7),
            anchor: new google.maps.Point(4, 4)
          },
          title: 'Move me!'
        });

        // Bind the marker map property to the DistanceWidget map property 
        marker.bindTo('map', this);

        // Bind the marker position property to the DistanceWidget position // property 
        marker.bindTo('position', this);

        // Create a new radius widget var radiusWidget = newRadiusWidget();

        // Bind the radiusWidget map to the DistanceWidget map 
        radiusWidget.bindTo('map', this);

        // Bind the radiusWidget center to the DistanceWidget position 
        radiusWidget.bindTo('center', this, 'position');

        // Bind to the radiusWidgets' distance property this.bindTo('distance', radiusWidget);

        // Bind to the radiusWidgets' bounds property this.bindTo('bounds', radiusWidget);
      }
      DistanceWidget.prototype = new google.maps.MVCObject();

      /** 
       * A radius widget that add a circle to a map and centers on a marker.
       *
       * @constructor
       */functionRadiusWidget() {
        var circle = new google.maps.Circle({
          strokeWeight: 2
        });

        // Set the distance property value, default to 50km. this.set('distance', 50);

        // Bind the RadiusWidget bounds property to the circle bounds property. this.bindTo('bounds', circle);

        // Bind the circle center to the RadiusWidget center property 
        circle.bindTo('center', this);

        // Bind the circle map to the RadiusWidget map 
        circle.bindTo('map', this);

        // Bind the circle radius property to the RadiusWidget radius property 
        circle.bindTo('radius', this);

        this.addSizer_();
      }
      RadiusWidget.prototype = new google.maps.MVCObject();


      /** 
       * Update the radius when the distance has changed.
       */RadiusWidget.prototype.distance_changed = function() {
        this.set('radius', this.get('distance') * 1000);
      };
      /** 
       * Add the sizer marker to the map.
       *
       * @private
       */RadiusWidget.prototype.addSizer_ = function() {
        var sizer = new google.maps.Marker({
          draggable: true,
          icon: {
            url: "https://maps.gstatic.com/intl/en_us/mapfiles/markers2/measle_blue.png",
            size: new google.maps.Size(7, 7),
            anchor: new google.maps.Point(4, 4)
          },
          title: 'Drag me!'
        });

        sizer.bindTo('map', this);
        sizer.bindTo('position', this, 'sizer_position');

        var me = this;
        google.maps.event.addListener(sizer, 'drag', function() {
          // Set the circle distance (radius) 
          me.setDistance();
        });
      };

      /** 
       * Update the center of the circle and position the sizer back on the line.
       *
       * Position is bound to the DistanceWidget so this is expected to change when
       * the position of the distance widget is changed.
       */RadiusWidget.prototype.center_changed = function() {
        var bounds = this.get('bounds');

        // Bounds might not always be set so check that it exists first. if (bounds) {
          var lng = bounds.getNorthEast().lng();

          // Put the sizer at center, right on the circle. var position = new google.maps.LatLng(this.get('center').lat(), lng);
          this.set('sizer_position', position);
        }
      };

      /** 
       * Calculates the distance between two latlng locations in km.
       * @see http://www.movable-type.co.uk/scripts/latlong.html
       *
       * @param {google.maps.LatLng} p1 The first lat lng point.
       * @param {google.maps.LatLng} p2 The second lat lng point.
       * @return {number} The distance between the two points in km.
       * @private
       */RadiusWidget.prototype.distanceBetweenPoints_ = function(p1, p2) {
        if (!p1 || !p2) {
          return0;
        }

        var R = 6371; // Radius of the Earth in km var dLat = (p2.lat() - p1.lat()) * Math.PI / 180;
        var dLon = (p2.lng() - p1.lng()) * Math.PI / 180;
        var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.cos(p1.lat() * Math.PI / 180) * Math.cos(p2.lat() * Math.PI / 180) * Math.sin(dLon / 2) * Math.sin(dLon / 2);
        var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
        var d = R * c;
        return d;
      };


      /** 
       * Set the distance of the circle based on the position of the sizer.
       */RadiusWidget.prototype.setDistance = function() {
        // As the sizer is being dragged, its position changes.  Because the // RadiusWidget's sizer_position is bound to the sizer's position, it will // change as well. var pos = this.get('sizer_position');
        var center = this.get('center');
        var distance = this.distanceBetweenPoints_(center, pos);

        // Set the distance property for any objects that are bound to it this.set('distance', distance);
      };

      functiondisplayInfo(widget) {
        var info = document.getElementById('info');
        info.innerHTML = 'Position: ' + widget.get('position').toUrlValue(3) + ', distance: ' + widget.get('distance').toFixed(3);
      }

html,
body,
#map-canvas {
  height: 100%;
  margin: 0px;
  padding: 0px
}

<scriptsrc="https://maps.googleapis.com/maps/api/js?libraries=geometry"></script><divid="info"></div><divid="map-canvas"></div>