KML Network Link - Fly To

Question

I am developing an application that launches Google Earth with a KML file that links to other local files via <NetworkLink>, which does Time Interval refreshing. I'm trying to define a KML file that will center the map (fly to) a specific location.

Network Link has a tag which flies to the first placemark or FlyTo within the file. However, this would execute the fly to whenever the file is refreshed, which in my case, is when the Time Interval expires. Is there some way that I can have the fly-to command execute only when the linked network file changes, rather than every time? Is there any way to have the Fly To process only once until the linked file is changed somehow? My NetworkLink file is defined as follows:

  <NetworkLink>
    <name>My Fly To Request</name>
    <Link>
      <href>MyFlyTo.kmz</href>
      <refreshMode>onInterval</refreshMode>
      <refreshInterval>2</refreshInterval>
    </Link>
  </NetworkLink>  

The application will frequently update the the specific placemark to be centered on when the user requests. It is not a static placemark that needs to be centered on, but one that will change frequently.

Answer 1

I believe you could achieve this by using a combination of ID attributes and the NetworkLinkControl and Update element in Kml.

The MyFlyToRequest.kml file contains the NetworkLink that loads the data file, which contains your data, it has the flyToView element set to true. Notice too the network link also has an id of request

MyFlyToRequest.kml

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
<NetworkLink id="request">
    <name>My Fly To Request</name>
    <Link>
      <href>http://www.yourserver.com/MyFlyTo.kmz</href>
      <refreshMode>onInterval</refreshMode>
      <refreshInterval>2</refreshInterval>
    </Link> 
    <flyToView>1</flyToView>   
</NetworkLink>
</kml>

The second file, MyFlyTo.kmz, is the one loaded. It has your current data as is..,However, it would also have an additional NetworkLink that loads a new third file.

MyFlyTo.kmz - Edited

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
<Document id="data">
  <visibility>1</visibility>
  <NetworkLink>
    <name>Update MyFlyToRequest</name>
    <Link>
      <href>http://www.yourserver.com/TurnOffFlyTo.kml</href>
    </Link>
  </NetworkLink>
  <Placemark>
    <name>This is flown to once (hopefully)</name>
      <Point>
        <coordinates>52,0,0</coordinates>
      </Point>
   </Placemark>
</Document>
</kml>

The new third file TurnOffFlyTo.kml is part of the key to the set up, it contains a NetworkLinkControl that targets the request NetworkLink in the first MyFlyToRequest.kml file. It simply sets flyToView element to 0.

TurnOffFlyTo.kml

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
<NetworkLinkControl>
  <Update>
    <targetHref>http://www.yourserver.com/MyFlyToRequest.kml#request</targetHref>
    <Change>
        <NetworkLink id="request">
            <!-- turn off the flyto behaviour -->
            <flyToView>0</flyToView>   
        </NetworkLink>
    </Change>
  </Update>
</NetworkLinkControl>
</kml>

The final file TurnOnFlyTo.kml simply retoggles the flyto behaviour again.

TurnOnFlyTo.kml

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
<NetworkLinkControl>
  <Update>
    <targetHref>http://www.yourserver.com/MyFlyToRequest.kml#request</targetHref>
    <Change>
        <NetworkLink id="request">
            <!-- turn off the flyto behaviour -->
            <flyToView>1</flyToView>   
        </NetworkLink>
    </Change>
  </Update>
</NetworkLinkControl>
</kml>

The logic is as follows.

1. MyFlyToRequest.kml loads MyFlyTo.kml
2. flyto is enabled so the view moves the first first placemark, etc, in MyFlyTo.kml
3. The link in MyFlyTo.kml loads TurnOffFlyTo.kml.
4. The Update in TurnOffFlyTo.kml three disables flyto in MyFlyToRequest.kml.
5. File one, refreshes, loads file two...

If you need to re-enable the flyto, you would simply load File four. If the data in MyFlyTo.kmz is being generated by you it would be a simple case of loading TurnOnFlyTo.kml right where TurnOffFlyTo.kml was called.

All that said, this is not tested and as such might not work as is, although in principal I don't see why it wouldn't.

If it sounds like something you might try here are a few resources that should help.

NetworkLinkControl Reference

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

Using Updates

http://code.google.com/apis/kml/documentation/updates.html