Wednesday, September 24, 2008

Timeline HowTo

The timeline is the feature of Google Earth that allows time animation. The screen shot below shows some time tagged placemarks of a group of our geography students going up the Arrolla glacier earlier this month*

Animation of a student field work hike up a glacier near Arrolla

Arrolla Glacier Walk GEarth File

The Google timeline documentation is fairly useful for the basics but leaves users a bit confused over some issues so here are some timeline tips:

Can't get the timeline to show? To get the timeline to show you need to have time stamped data somewhere in your places column. The relevant data must also be visible (i.e. radio button ticked in the places column).

Timeline is visible but not showing what you expected? Once the timeline is visible:
1. Click the clock icon on its far left and select 'restrict time to currently selected folder'.
2. Click the folder (or sub folder) in the places column holding the data you want to view
3. The folder should get a blue background. Make sure its radio button is clicked too.
4. Check if the timeline is now working as expected, if not go onto time range tip.

Time range tip: The timeline shows the complete range of data from the oldest to the youngest time stamped data in your selected folder (if you have selected 'restrict time to current folder' option as listed above).

Imagine you have selected and ticked a parent folder (selected folders have a blue background) that holds 3 sub folders. The 3 sub folders contain GPS data from 1st of May 1975, 2 July 2008 and 1 Sep 2008 respectively. In this situation the timeline will animate from 1 May 1975 to 1 Sep 2008; if you click the 'play' button on the timeline the data from 1 May 75 will briefly show on screen, then nothing will show at all as the timeline animates through all the days from 2 May 75 to 1 Jul 08. Finally there will be a brief flash of data as the timeline passes 2 Jul and 1 Sep.

The solution is to untick certain folders within a parent folder so that a smaller time range is shown. Alternatively, select and tick a subfolder instead of the parent folder.

Shadow Shading: Just to show what it could do, I turned on the 'sunlight' button on in Google Earth and captured the effect in the film clip. It shades the backs of the mountains quite nicely but looks odd because it fails to animate the shadow that the peak (center right of screen) cast over the valley at the time the imagery was acquired.

*The GPS automatically recorded their position every 2 seconds, each of these data points plots as a placemark. The timeline shows a 'spread of time' so at any point in the animation you will see a number of placemarks showing. If they're bunched together, the group was slow moving or stationary. If they are spread apart it shows the group was moving at speed. Where the placemarks dissapear altogether its because the GPS lost signal because of the mountains.

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