Question

I would like to draw an ellipse on google maps based off four coordinates, like the current “rectangle” method available via the API:

var rectangle = new google.maps.Rectangle({
          strokeColor: '#FF0000',
          strokeOpacity: 0.8,
          strokeWeight: 2,
          fillColor: '#FF0000',
          fillOpacity: 0.35,
          map: map,
          bounds: new google.maps.LatLngBounds(
            new google.maps.LatLng(33.671068, -116.25128),
            new google.maps.LatLng(33.685282, -116.233942))
        });

(using the bounds paramater).

If that fails, is there an easy way to convert the distance between 2 polygons to a unit of measurement?

Answer 1

You have to calculate the path yourself. This should help:

http://mathworld.wolfram.com/Ellipse.html

Edit: This might be more useful:

http://www.geocodezip.com/v3_MW_example_eshapes.html

A v3 port of Mike Williams’ v2 eshapes library, supports ellipse (but not based on the bounds).

Working example that sizes to the map bounds.

proof of concept fiddle

code snippet:

var map = null;

var myOptions = {
  zoom: 8,
  center: new google.maps.LatLng(43, -79.5),
  mapTypeControl: true,
  mapTypeControlOptions: {
    style: google.maps.MapTypeControlStyle.DROPDOWN_MENU
  },
  navigationControl: true,
  mapTypeId: google.maps.MapTypeId.ROADMAP
}
map = new google.maps.Map(document.getElementById("map"),
  myOptions);

google.maps.event.addListenerOnce(map, "bounds_changed", function() {
  var bounds = map.getBounds();
  var major_axis = google.maps.geometry.spherical.computeDistanceBetween(bounds.getNorthEast(), new google.maps.LatLng(bounds.getSouthWest().lat(), bounds.getNorthEast().lng())) / 2;
  var minor_axis = google.maps.geometry.spherical.computeDistanceBetween(
    new google.maps.LatLng(bounds.getCenter().lat(), bounds.getSouthWest().lng()),
    new google.maps.LatLng(bounds.getCenter().lat(), bounds.getNorthEast().lng())) / 2;

  // === Ellipse ===
  var point = map.getCenter(); // new google.maps.LatLng(43,-78);
  var ellipse = google.maps.Polygon.Ellipse(point, major_axis, minor_axis, 0, "#000000", 2, 1, "#ffff00", 0.5);
  ellipse.setMap(map);
});

// This Javascript is based on code provided by the
// Community Church Javascript Team
// http://www.bisphamchurch.org.uk/   
// http://econym.org.uk/gmap/

// EShapes.js
//
// Based on an idea, and some lines of code, by "thetoy" 
//
//   This Javascript is provided by Mike Williams
//   Community Church Javascript Team
//   http://www.bisphamchurch.org.uk/   
//   http://econym.org.uk/gmap/
//
//   This work is licenced under a Creative Commons Licence
//   http://creativecommons.org/licenses/by/2.0/uk/
//
// Version 0.0 04/Apr/2008 Not quite finished yet
// Version 1.0 10/Apr/2008 Initial release
// Version 3.0 12/Oct/2011 Ported to v3 by Lawrence Ross
google.maps.Polygon.Ellipse = function(point, r1, r2, rotation, strokeColour, strokeWeight, Strokepacity, fillColour, fillOpacity, opts) {
  rotation = rotation || 0;
  return google.maps.Polygon.Shape(point, r1, r2, r1, r2, rotation, 100, strokeColour, strokeWeight, Strokepacity, fillColour, fillOpacity, opts)
}

google.maps.Polygon.Shape = function(point, r1, r2, r3, r4, rotation, vertexCount, strokeColour, strokeWeight, Strokepacity, fillColour, fillOpacity, opts, tilt) {
  var rot = -rotation * Math.PI / 180;
  var points = [];
  var latConv = google.maps.geometry.spherical.computeDistanceBetween(point, new google.maps.LatLng(point.lat() + 0.1, point.lng())) * 10;
  var lngConv = google.maps.geometry.spherical.computeDistanceBetween(point, new google.maps.LatLng(point.lat(), point.lng() + 0.1)) * 10;
  var step = (360 / vertexCount) || 10;

  var flop = -1;
  if (tilt) {
    var I1 = 180 / vertexCount;
  } else {
    var I1 = 0;
  }
  for (var i = I1; i <= 360.001 + I1; i += step) {
    var r1a = flop ? r1 : r3;
    var r2a = flop ? r2 : r4;
    flop = -1 - flop;
    var y = r1a * Math.cos(i * Math.PI / 180);
    var x = r2a * Math.sin(i * Math.PI / 180);
    var lng = (x * Math.cos(rot) - y * Math.sin(rot)) / lngConv;
    var lat = (y * Math.cos(rot) + x * Math.sin(rot)) / latConv;

    points.push(new google.maps.LatLng(point.lat() + lat, point.lng() + lng));
  }
  return (new google.maps.Polygon({
    paths: points,
    strokeColor: strokeColour,
    strokeWeight: strokeWeight,
    strokeOpacity: Strokepacity,
    fillColor: fillColour,
    fillOpacity: fillOpacity
  }))
}

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

<script src="https://maps.googleapis.com/maps/api/js?libraries=geometry&key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk"></script>
<div id="map"></div>