How to display a moving boat in Google Earth?

Question

I am new to the KML format and try to figure out how to display a boat (a png), moving from a place to another along a path (a simple line drawn composed of several lines).

I can see how to display a Placemark, even with an icon, and a Path, separately.

What I would like to see when I click on the KML file is :

• the boat appearing at the departure point;
• the path drawing itself until the arrival;
• the boat icon moving at a comfortable speed (bonus point it I can set a ration time / progress, extra bonus if I can click on start, pause or rewind) from departure to arrival along the path.

Is that even possible ? I know it is with Google Map, but you can program it with Javascript, which eases things a lot.

Answer 1

This is an old question, and there is now a better way to move a placemark (or even better a model) along a pre-determined linestring. Look into using this feature:

http://code.google.com/apis/kml/documentation/kmlreference.html#gxtrack

Sample code:

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2"
xmlns:gx="http://www.google.com/kml/ext/2.2">
<Folder>
  <Placemark>
    <gx:Track>
     <when>2010-05-28T02:02:09Z</when>
     <when>2010-05-28T02:02:35Z</when>
     <when>2010-05-28T02:02:44Z</when>
     <when>2010-05-28T02:02:53Z</when>
     <when>2010-05-28T02:02:54Z</when>
     <when>2010-05-28T02:02:55Z</when>
     <when>2010-05-28T02:02:56Z</when>
     <gx:coord>-122.207881 37.371915 156.000000</gx:coord>
     <gx:coord>-122.205712 37.373288 152.000000</gx:coord>
     <gx:coord>-122.204678 37.373939 147.000000</gx:coord>
     <gx:coord>-122.203572 37.374630 142.199997</gx:coord>
     <gx:coord>-122.203451 37.374706 141.800003</gx:coord>
     <gx:coord>-122.203329 37.374780 141.199997</gx:coord>
     <gx:coord>-122.203207 37.374857 140.199997</gx:coord>
   </gx:Track>
 </Placemark>
</Folder> 
</kml>

Answer 2

The only way I've been able to make this work in static KML is to interpolate between the start and stop points and add placemarks for each frame I want to animate. So, from t=0 to t=1, draw a placemark at the start point. From t=1 to t=2, draw a placemark at the next point, etc.

This gives you the temporal player bar in Google Earth and you can rewind or advance the animation. However it is a little annoying because you wind up with every interpolation point in your placemark tree. Putting the placemarks in their own folder keeps them out of the way, but there's no way to hide them from the user.

Take a look at http://code.google.com/apis/kml/documentation/time.html#animating The whale shark example does more or less what you want for the placemark. (The URL for the marker icon is broken). Animating the progress along the track can be done using the same trick.

If you want to try something much more difficult, you can try serving dynamic KML. Have Google Earth load a network link to your initial data. Then load another network link with an that sends an update for your placemark at every time tick.

• http://code.google.com/apis/kml/documentation/kmlreference.html#link
• http://code.google.com/apis/kml/documentation/updates.html

This approach has some serious disadvantages because it requires an external program to drive Google Earth and it does not give the user access to the built-in Google Earth temporal player bar. It also requires that all the data be loaded over a network link -- KML data from a file cannot be updated. That means your driver program needs to act as a http server. Also, in this model it is very hard to know exactly when Google Earth has finished loading and drawing the update. Really I don't recommend doing this; you can make it work using the Google Earth COM API, but it will always be a fragile solution.

Answer 3

There's a browser plug-in that lets you embed Google Earth into a browser page. From there you can use JavaScript to animate your placemark, change your paths, etc. Check out the Google Earth API Developer's Guide.