This is the third post in our series on animating in Google Earth
Today we are looking at how the Google Earth time toolbar works.
The Google Earth time toolbar is used in three different instances and works slightly differently in each case:
- When you open ‘Historical imagery’.
- When you turn on the ‘show sunlight’ option (rising sun icon on the Google Earth toolbar).
- When you open a KML file that has time data attached to its contents. The time data for a given item may be either a specific point in time or a span of time.
- The ‘+’ and ‘-‘ symbols allow you to zoom in or out of the toolbar. This is especially useful if you have a large KML file with a lot of time-stamped features and need to select a specific time, or in ‘historical imagery’ when there are a large number of images for the location you are viewing.
- The play / pause button causes the toolbar to automatically run from left to right (past to future) along the timeline. How fast it plays and whether or not it repeats depend on the settings discussed below.
- The spanner icon opens the settings window.
- The ‘x’ closes the time toolbar. When you are in ‘historical imagery’ or ‘sunlight’ mode, this has the effect of turning off the feature and going back to the default view. When you have a time-stamped KML item selected the ‘x’ is greyed out and you cannot close the toolbar.
- and 6. The ends of the toolbar have buttons that move the slider by increments. What an increment is depends on the mode you are in. In historical imagery mode this moves between available images. In the other two modes it moves by a fraction (about one sixtieth) of the toolbar.
The date represented by each end is shown below the ends.
- and 8. In ‘historical imagery’ mode and ‘sunlight’ mode, there is a single slider showing the point in time being displayed. The slider can be dragged along the toolbar to show a different time or you can click on any point on the toolbar to jump directly to that time.
Understanding the slider is critical for time based animations.
When you have a KML file with time-stamped data, then the slider has two parts. When they are separated, Google Earth displays all items with a time-stamp between the two sliders. If your data has single time-stamps then it is necessary to separate the two sliders a bit or you will never see the data. How much you separate them affects how long each time-stamped item will show for during an animation. If your data has time ranges instead of single time-stamps then it is better to have the sliders clamped together.
The settings dialog box allows you to select the start and end times shown on the toolbar, select the timezone to use, adjust the speed of the animation (when you press the play button) and whether or not to repeat the animation. The speed adjustment is just a slider and affects how quickly the slider gets from one end of the time toolbar to the other. It appears to be unrelated to the actual length of time being displayed. This can make it difficult to make animations with an exact speed.