Google Maps v3 setting a circle with editable radius but not center

Question

I have managed to put a circle on a map and make it editable:

var circle = new google.maps.Circle({
          map: map,
          radius: 1609.344, // 1 mile         


        

Answer 1

You can try listening for the center_changed event and when it fires reposition the center, for example:

Global variables:

    var centerPoint = new G.LatLng(45.5, -100.5);
    var ignore = false;
    var poly;
//position the map where the circle is so we can see it.
    map.setCenter(centerPoint);
    map.setZoom(11);

and then:

poly = new google.maps.Circle({
    map: map,
    center:centerPoint,
    radius: 1609.344, // 1 mile
    editable: true,
    fillOpacity: 0.25
});

G.event.addListener(poly,'center_changed',function(){
    if (ignore){
        ignore = false;
        return;
    }
    poly.setEditable(false);
    ignore = true;
    poly.setCenter(centerPoint);
    poly.setEditable(true);
});

The only problem is that the center marker may be misleading to the user.

Answer 2

See this article from the documentation (before editable objects). If you take the step 6 and don't make the center marker draggable, I think it is what you want.

fiddle containing original code from link

code snippet:

/**
 * 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 to attach to.
 *
 * @constructor
 */
function DistanceWidget(map) {
  this.set('map', map);
  this.set('position', map.getCenter());

  var marker = new google.maps.Marker({
    // draggable: true,  // <-- change to make so position doesn't move
    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 = new RadiusWidget();

  // 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
 */
function RadiusWidget() {
  var circle = new google.maps.Circle({
    strokeWeight: 2
  });

  // Set the distance property value, default to 10km.
  this.set('distance', 10);

  // 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);

  // Add the sizer marker
  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,
    title: 'Drag me!'
  });

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

  var me = this;
  google.maps.event.addListener(sizer, 'drag', 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 min = 0.5;
    var max = 15;
    var pos = me.get('sizer_position');
    var center = me.get('center');
    var distance = google.maps.geometry.spherical.computeDistanceBetween(center, pos) / 1000;
    if (distance < min) {
      me.set('sizer_position', google.maps.geometry.spherical.computeOffset(center, min * 1000, google.maps.geometry.spherical.computeHeading(center, pos)));
    } else if (distance > max) {
      me.set('sizer_position', google.maps.geometry.spherical.computeOffset(center, max * 1000, google.maps.geometry.spherical.computeHeading(center, pos)));
    }
    // 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);
  }
};


/**
 * 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 = google.maps.geometry.spherical.computeDistanceBetween(center, pos) / 1000;

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


function init() {
  var mapDiv = document.getElementById('map-canvas');
  var map = new google.maps.Map(mapDiv, {
    center: new google.maps.LatLng(37.790234970864, -122.39031314844),
    zoom: 11,
    mapTypeId: google.maps.MapTypeId.ROADMAP
  });
  var distanceWidget = new DistanceWidget(map);

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

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

function displayInfo(widget) {
  var info = document.getElementById('info');
  info.innerHTML = 'Position: ' + widget.get('position') + ', distance: ' +
    widget.get('distance');
}

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

#map-canvas {
  height: 500px;
}

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

original article (link now dead)