cache

We have recently been catching up on the outlines for our KML of Google Earth 3D areas. The internet speeds here in Cape Town increase every year, but we still seem to spend a lot of time waiting for Google Earth imagery to load. When tracing out 3D areas, we have found it helpful to pre-cache an area before starting to draw and we thought we should share the technique, as our readers could find it useful in a variety of circumstances.

The border of the 3D imagery areas is often quite intricate.

The basic technique is very simple. Just draw a path where you wish to pre-cache imagery, then select the path and click the ‘Play Tour’ button that appears. Once the tour starts, go away and do something else for a while then come back when it is finished and you will find that imagery in the area you are interested in now loads much faster.

A ‘Play Tour’ button appears in the divider between Places and Layers whenever you select a path.

The default settings have the Google Earth ‘Camera’ follow the line quite closely and thus only imagery very near the line is cached. In addition, depending on the speed of your internet connection, the camera may move a bit too fast to fully cache the imagery before moving on. However, this can be adjusted with the settings found in Tools->Options->Touring:

We like to set the Camera Tilt Angle to zero (looking straight down) and the Camera Range to 1000 metres. Start the tour and see if the imagery is managing to load completely before it goes off screen. If not, reduce the Speed setting.

The above technique can also be used if you plan to use Google Earth offline, as you can pre-cache an area by drawing a zigzag path across it. Be sure to test it before setting off on a long journey.

To learn more about Google Earth’s cache see some of our previous posts on the topic.

The cache system in Google Earth is something you rarely think about, but it’s vitally important to how you use the product. By caching the imagery (and roads, buildings, etc), Google Earth is able to provide a very smooth experience once the data has loaded onto your system.

Google Earth keeps imagery in two types of caches to help improve performance. The Memory Cache holds imagery in your RAM, and is cleared each time you start up Google Earth. The Disk Cache holds imagery on your hard drive for easier access. Incresing those numbers can help your performance. However, if you have a low amount of RAM or are low on hard drive space, you may be better off to decrease them a bit to give your computer a little more to work with.

Using the cache you can also use Google Earth offline to some degree. It’s not as robust as the upcoming Google Maps offline features, but it’s still pretty cool.

Frank summarized the system pretty well in this post from a few years ago. In part:

First, go to the menu item Tools->Options and select the “Cache” tab. You will not need to change the memory cache for viewing the cache (there is a trick for storing the cache with this setting – see below). The memory cache is set automatically based on your system’s memory. You can make the disk cache size as large as 2000 MB (i.e. 2 Gigabytes). This will give you more data to work with. Then, you need to move to the area you want data for and zoom into that area. The most recent things you have looked at will be what’s in your cache. It’s important you zoom to the closest view you think you’ll use. Turn on other layers for information you want cached (for example, ‘Terrain‘, ‘Roads‘ and ‘Borders‘ – the more you select, the faster the cache wil fill). Also, make sure you save any KML files you might want to use in files on the same computer.

The more data you cache, the sooner the cache will fill, so be cautious. If you’re going on a long trip, cache in high resolution imagery just the areas where you plan to use GE for close viewing. Avoid turning other layers if you only need imagery. It can be a pain to move around and capture an area of imagery at full high resolution and load up your cache properly.

As a general rule I turn the cache up as high as possible to help improve my experience with Google Earth, and in most cases I’d suggest you do the same.

Some of you out there are running brand new, amazingly fast machines that can handle anything you throw at it and Google Earth consistently runs well. For the rest of us, though, we need to balance features vs. speed in order to keep things running smoothly.
With that in mind, here are some tips to help Google Earth run more smoothly on your computer.
DirectX vs. OpenGL (Windows only)
On Windows computers, you have a choice to run Google Earth in “DirectX” or “OpenGL” mode. You can change the setting from inside of the [Tools] –> [Options] menu, or start them separately from your main Start menu. There may not be much of a difference, but play with them and see what happens.
Disable some layers/places
If you’re running with a whole bunch of Layers and Places open, try turning a few off. I enjoy keeping the Blue Marble overlay on quite often, along with a handful of other layers (roads, borders, 3D buildings, etc). However, things speed up considerably if I turn all of that off.
3D buildings are one of the biggest performance hogs, simply because they generate a lot of data to be displayed, so turning them off will help quite a bit. On the other hand, if you’re wanting to find ways to improve 3D building performance, then disabling as many other layers as possible is your best move.
Anisotropic Filtering
Anisotropic filtering is one of those cool features in Google Earth that most people don’t understand. In short, it helps keep things sharp when you’re viewing imagery from a low angle. Here is an image from the anisotropic filtering Wikipedia entry, comparing it turned off (on the left) and on (on the right):

You can see that it certainly helps make things look better, but it also costs a bit of performance. Turning it off can help speed things up.
Antialiasing
Anti-aliasing is a technique used to smooth the edges of features in an image. In Google Earth, this is particularly noticeable on 3D models. For example, here is part of the Georgia Aquarium with Google Earth’s Antialiasing set to “medium” on the left and “off” on the right. You can clearly see how much it improves the appearance of the building, though turning it off will help things to run a bit more smoothly. You can turn it off in the main [Tools] –> [Options] menu.

Terrain Quality
The entire globe in Google Earth is covered with a 3D terrain mesh. But adjusting the quality of that mesh, you can improve performance. Simply go to [Tools] –> [Options] and move the Terrain Quality slider further to the left.
Atmosphere
When zoomed out, Google Earth has a cool blue/gray atmosphere surrounding the earth. You can disable it by clicking on [View] –> [Atmosphere].
Water Surface
When Google Earth 5 was released, one of the big new features was the 3D ocean. Part of that new feature includes a realistic looking surface on the ocean. To disable that surface, go to [View] –> [Water Surface].
Cache
Google Earth keeps imagery in two types of caches to help improve performance. The Memory Cache holds imagery in your RAM, and is cleared each time you boot up your computer. The Disk Cache holds imagery on your hard drive for easier access. Incresing those numbers can help your performance. However, if you have a low amount of RAM or are low on hard drive space, you may be better off to decrease them a bit to give your computer a little more to work with.
None of these tips will make a huge difference by themselves, aside from any massive “Place” that you may have enabled, but added up they can make quite a difference. Play with some of the settings and see what happens.
If you think of any tips that I’ve missed, leave a comment and let us know!