EMS : Geometry

Geometry types are vector-based spatial objects that can be plotted on a map. Typically, geometry objects are used to represent boundaries and paths. There are several types, including the Point, LineString and Polygon. A route line is an example of a LineString geometry.

Types

The following types of geometry are available.

The Basics

 The following code snippet demonstrates how to add a new vector layer to your map, create a feature with basic point geometry, and add it to the layer. This snippet assumes you have a map.

var layer = new EMS.Layer.Vector("Vectors");
map.addLayers([layer]);

var lonlat = new EMS.LonLat(144.9, -37.9);
var geometry = new EMS.Geometry.Point(lonlat);
var feature = new EMS.Feature.Vector(geometry);.
layer.addFeatures([feature]);

Line Geometry

To create a more complex geometry such as a LineString, construct a geometry object, passing in a list of EMS.LonLat objects. The following code snippets show you how.

var lonlats = [
 new EMS.LonLat(144.9, -37.9),
 new EMS.LonLat(144.7, -37.9),
 new EMS.LonLat(144.8, -37.8)
];
var geometry = new EMS.Geometry.LineString(lonlats);
...

Polygon Geometry

To construct a polygon, first create a LinearRing, or rings, and add them as a list to your Polygon constructor. Similarly, to construct a MultiPolygon geometry you will need a list of Polygons.

var lonlats = [
 new EMS.LonLat(144.9, -37.9),
 new EMS.LonLat(144.7, -37.9),
 new EMS.LonLat(144.8, -37.8)
];
var linearRing = new EMS.Geometry.LinearRing(lonlats);
var geometry = new EMS.Geometry.Polygon([linearRing]);
...

Custom Styling

To override style elements, include a style when you construct your feature

var style = OpenLayers.Util.applyDefaults(
   {
     strokeColor: "#0000ff", 
     strokeWidth: 4
   },
   OpenLayers.Feature.Vector.style['select']
);
var geometry = new EMS.Geometry.Point(lonlat);
var feature = new EMS.Feature.Vector(geometry, null, style); 
...

Attributes

For each feature you can attach an additional attributes object, which can be extra information about the feature, or anything you like. For example:

var attributes = {
   name:"My Feature",
   id: 123,
   type: "Parks and Gardens"
};
var feature = new EMS.Feature.Vector(geometry, attributes);
...