Question

I made a large KML file ca. 23 MBytes long. Google Earth renders it very long period of time, lags and occupies 1GB RAM and more. On slower computers it may also not to render some areas.

So the idea is to use a parametrized GET request to the server returning kml data only for a region with specified boundaries.

Can GoogleEarth initiate and use such requests?

Answer 1

What you’re asking can be done with a NetworkLink. If you dynamically generate the KML from a servlet, web-service, script, etc. then you can instruct Google Earth to send the bounding box for its view from which you can generate the KML to return. This approach requires hosting a custom “service” on an application server/web server that can generate KML in response to requests sent by Google Earth.

In your root-level NetworkLink you need to define refreshMode=onChange to refesh when view is changed along with the URL to the servlet. Recommended to set viewRefreshMode=onStop with a viewRefreshTime element so the data is only fetched 1 second after the user stops zooming/moving around otherwise the data is continually refreshed. Also the viewFormat is needed to instruct Google Earth to return the bounding box of the view. In this example, the BBOX parameter is added to the HTTP parameters sent to the servlet in an HTTP GET request.

<Link>
      <href>servlet-url</href>
      <refreshMode>onChange</refreshMode>
      <viewRefreshMode>onStop</viewRefreshMode>
      <viewRefreshTime>1</viewRefreshTime>
      <viewFormat>BBOX=[bboxWest],[bboxSouth],[bboxEast],[bboxNorth]</viewFormat>
</Link>

If your data spans a large area then you could break up the data into separate KML files then specify Region-based NetworkLinks in parent KML file. This approach would allow you to generate the data once as static KML files and only serve up what data is “active” based on the user’s view.

Related Tutorial:

https://developers.google.com/kml/documentation/regions#regionbasednl

Reference:

https://developers.google.com/kml/documentation/kmlreference#networklink
https://developers.google.com/kml/documentation/kmlreference#region
https://developers.google.com/kml/documentation/kmlreference#viewformat