Google Earth Overlays
Google Earth can display online images as an overlay above the satellite imagery without requiring any special server software. There are only a few requirements:
- High resolution images must be tiled to be displayed at their full resolution
- A Keyhole Markup Language (KML) file containing the positioning information and url of the image(s)
e.g. the KML file for a map of Melbourne (1855).
The demonstrations on this page were created using freely available software. The steps taken to produce them are outlined below, although with access to the appropriate mapping expertise more efficient methods could be set up. The MMBW map in the video was georeferenced entirely in GlobalMapper.
- A low resolution (5000 pixels high) version of the map was manually added as an overlay in Google Earth for positioning
- Adjust transparency to 50%
- Reposition each corner of the overlay to visually align features on the map with the underlying satellite imagery
- Record the coordinates of the 4 corners of the image
- Add the positioning information to the high resolution of the image (georeference) using gdal_translate from OS4GeoW
- The georeferenced image was then tiled using Map Tiler which also generates the required KML files to display the tiled image set.
- Upload all of the files to a web server