The last post covered the basics of the Google Earth disk cache, and how it lets you use Google Earth even when you don’t have an Internet connection. Today I’ll talk about the simplest method to create a Google Earth disk cache file for an area – doing it manually
To create a localized Google Earth cache file manually:
1. Start up Google Earth while connected to the Internet
2. Go to Tools => Options, and select the Cache tab:
3. Click the “Clear disk cache” button to remove all data from the cache and cache index files. This maximizes the available amount of space for your cached data, so that you can cover more area with the cached data.
4. Set the Memory Cache Size to the minimum allowable value of 16MB; this will force Google Earth to put data in the disk cache more quickly. Click the “Clear memory cache” button, then exit the Options screen
5. In Google Earth, navigate to your area of interest.
6. Set your viewing altitude (the “Eye alt”) for the desired imagery resolution. Higher altitudes mean lower resolution, but the data will take up less space. Lower altitudes give you higher image resolution, but at the cost of more disk space. If there are major changes in elevation over the area, you may have to change your altitude to match them to keep your relative height; if the terrain elevation drops, but your “eye alt” stays the same, the image resolution will decrease because you are further away from the surface.
7. Wait for the “data loading” indicator at lower right to show that all the data for that area and resolution has been downloaded; it will display as a solid light-blue circle when downloading is complete for that area. You’ll also see the imagery change from blurry to sharp.
8. With the mouse or cursor keys, move the view to an adjacent area that overlaps the first area at least partially, and wait for the “data loading” indicator to show once again that all the data has been downloaded.
9. Repeat this process until you’ve covered your entire area of interest.
10. If want data at several different resolution levels, you could repeat steps 5-9, but at different viewing altitudes.
11. When you’re finished with steps 5-10, you might consider zooming all the way in to the closest level at one point, then all the way out to the planetary view level. It seems to me that this prompts Google Earth to write all of its data cached in RAM to the disk cache, but I could be wrong about this. It also seems as though there can be a time delay between viewing a location, and when it’s cached to disk, so waiting 10 minutes after you’ve finished covering the area of interest might be a good idea.
You now have a set of Google Earth data for that area saved in the disk cache. If you take your computer offline and start up Google Earth, it will tell you that it can’t log on to the server and download data, but it can still read in whatever data it has in the cache. You can copy this cached data (see this previous post for where to find it) into a different directory, and then copy it back into the cache directory when you need it, or even copy it to a different computer.
For small areas, manual caching of data won’t take too long, but for larger areas, manually scrolling to an area, waiting for the data to download, then scrolling to another area gets old very quickly. Fortunately, there are several free applications that can partially automate the process, and I’ll cover some of those in the next few posts.