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Archive for October 13th, 2016

Getting tiled maps into Google Earth

by Timothy Whitehead on Oct.13, 2016, under 3D Models, Argentina, Australia, Brazil, California, Denmark, England, Germany, Google Earth News, Google Earth Tips, Google Sky, Google maps, Hawaii, Indonesia, Ireland, Italy, Japan, Kenya, Mexico, Natural Landmarks, Netherlands, Sightseeing, Street Views, USA

[ Update: See this post for a KML to view to see the NOAA imagery in Google Earth. ]

Yesterday we had a look at some aerial imagery of the eastern coast of the US after Hurricane Matthew. The imagery comes from NOAA. We wondered what it would take to get the imagery into Google Earth. The NOAA has made the imagery available for viewing on this map and also offers the option to download it. However, the total size of all the imagery is over 24 GB. Also provided is the option to view the imagery as tiled data.

Most modern online maps use a fairly standardised method of tiling the map imagery. It is a relatively simple system that involves using the Mercator map projection and cutting off above 85.0511°N and below 85.0511°S, resulting in a map of the globe that is square. This is then divided into four squares, each of which is divided into four squares and so on. Each division is a zoom level. For the full technical details see this page.

Google Earth has a mechanism for presenting tiled data that is very similar to the above process. You can take a large image overlay and break it up into tiles in such a way that Google Earth only loads the tiles that are within the view and at a suitable resolution. The result is called a ‘Super-Overlay’. Google Earth Pro even has a built-in tool for creating these automatically which you can read more about here.

We already had some basic JavaScript code for working with map tiles that we created to work with Mapzen altitude data, which is available as map tiles. We combined this with information from the KML Developers Guide and technical information about the NOAA tiles and were able to create a Super-Overlay for a small portion of the NOAA data. And it works quite well. The problem is that it doesn’t scale.

You can download our sample here. It covers a short stretch of coast near Charleston, North Carolina. A Google Earth Super-Overlay actually consists of many KML files all network-linked to each other in a hierarchical fashion. Our sample file is actually in the compressed KMZ format and includes over 10,000 files which uncompressed are over 10 Mb. Keep in mind that the KML file does not contain any imagery at all, that is all coming directly from NOAA. When we tried to create larger Super-Overlays it crashed our JavaScript as the browser ran out of memory. We could probably find ways to generate larger Super-Overlays, but there is no getting around the file size, so it is practically impossible to do a single KML file for all the NOAA imagery.

The only real alternative would be to set up a server with all the Super-Overlay files. This would probably work quite well, but running a server in this particular instance is not worth it. What would be ideal would be for Google Earth to natively support map tiles such that you could give it the details of the tile server and it would handle it from there.


NOAA imagery as seen in Google Earth. Some flooding near Charleston, North Carolina.

The post Getting tiled maps into Google Earth appeared first on Google Earth Blog.

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