Google Maps with Google Earth Plugin



Fig 1 – Google Map with Google Earth plugin –

Google announced a new GE plugin for use inside Google Maps:
http://code.google.com/apis/earth/documentation/

This is an interesting development since it allows Google Earth to be used inside a browser. Google’s Map object can be programmed using their javascript api for user interaction control which was not available inside standalone Google Earth. The api documents have plenty of examples but the very simplest way to use the Google Earth Plugin is to simply load their plugin api javascript like this:

<script
	src="http://maps.google.com/maps?file=api&v=2.x&key=**************"
	type="text/javascript">
	google.load("earth", "1");
</script>

Then add a Map Type G_SATELLITE_3D_MAP to the Map control in the initialization code.

function initialize() {
	if (GBrowserIsCompatible()) {
		map = new GMap2(document.getElementById("map_canvas"));
		map.setCenter(new GLatLng(39.43551, -104.91207), 9);
     		var mapControl = new GMapTypeControl();
     		map.addControl(mapControl);
     		map.addControl(new GLargeMapControl());
     		map.addMapType(G_SATELLITE_3D_MAP);
	}
}

This adds a fourth map type, “Earth”, to the control shown over the Google map base.

Fig 2 – Google Map with Google Earth plugin showing map overlays

Now a user can switch to a GE type viewing frame with full 3D camera action. Unfortunately the Maptype control is hidden so returning back to a Map view requires an additional button and piece of javascript code:

function resetMapType(evt){
	map.setMapType(G_NORMAL_MAP);
}

In order to show how useful this might be I added a button to read kml from a url:

function  LoadKML(){
	var geoXml = new GGeoXml(document.getElementById('txtKML').value);
	GEvent.addListener(geoXml, 'load', function() {
		if (geoXml.loadedCorrectly()) {
			geoXml.gotoDefaultViewport(map);
			document.getElementById("status").innerHTML = "";
		}
	});
	map.addOverlay(geoXml);
	document.getElementById("status").innerHTML = "Loading...";
}

Now I simply coded up a servlet to proxy PostGIS datasources into kml for me and I can add mapOverlays to my hearts content. If I want to be a bit more SOA it would be simple to configure a Geoserver FeatureType and let Geoserver produce kml for me.

My LoadKML script lets me copy any url that produces kml into a text box, which then loads the results into the Google Map object. With the GE plugin enabled I can view my kml inside a GE viewer, inside my browser. By stacking these overlays onto the map I can see multiple layers. The javascript api gives me pretty complete control of what goes on. However, there are still some rough edges. In addition to overwriting the map control that would allow the user to click back to a map, satellite, or hybrid view, there are some very odd things going on with the kml description balloons. Since I’m using IE8beta I can’t really vouch for this being a universal oddity or some glitch in the IE8 situation. After all IE8 beta on Vista really does strange things to the Google Map website making it more or less unuseable.

Here are some items I ran across in the little bit of experimetation I’ve done:

  • plugin loading is slow and doesn’t appear to be cached
  • returning from Earth view requires javascript code
  • click descriptions are only available on point placemarks
  • the balloon descriptions show up only sometimes in an earth view
  • There appears to be a limit on the number of kml features which can be added. Over 5000 seems to choke

The rendering in the new Google Earth plugin view is quite useful and provides at least a subset of kml functionality. This evolution distinctly shows the advantage of a competitive market. The Microsoft Google competition significantly speeds the evolution of browser map technology. Microsoft is approaching this same type of browser merged capability as well with their pre announcement of Virtual Earth elements inside Silverlight. 3D buildings, Street view, Deep Zoom, Photosynth, Panoramio …. are all technologies racing into the browser. Virtual parallel worlds are fascinating especially when they overlap the real world. Kml feeds, map games, and live cameras coupled with GPS streams seem to be transforming map paradigms into more or less virtual life worlds.

GIS savvy developers already have a wealth of technology to expose into user applications. Many potential users, though, are still quite unaware of the possibilities. The ramp up of these new capabilities in the enterprise should make business tools very powerful, if not downright entertaining!

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