There are several different ways to automate animated historical imagery that we have explored in the past.
The first, and easiest, is to use a Google Earth Tour that simply changes the date by a given increment at a set frequency. So you could, for example, change the date by one month every second. In this post we presented some JavaScript to help with creating such tours. The main disadvantage of this technique is that Google Earth’s historical imagery is not regular and so you end up with periods of no imagery changes, and some skipped images. The technique does have the advantage of accurately representing the passage of time.
The second technique is to obtain the list of imagery dates using the Google Earth API and then use a tour to change the date, showing each existing image at a given frequency. This results in an animation that shows all the images in a given time range. We presented a tool for doing this in this post.
An outstanding problem that occurs with both techniques, is that Google Earth imagery is often not the best quality so you get an animation that includes some images with excessive cloud cover or updates that only cover part of the area of interest and do not look good. In addition, if you are trying to show change over time, you may not want images that are too close together in time if no significant differences can be seen between them. When we manually create animations for the blog we choose each image to include.
Some time ago we created a tool for creating Google Earth Tours that include or exclude images of your choice. We created it at the time the Google Earth API was expected to be shut down, so we chose not to share it. However, Google has so far kindly kept the Google Earth API alive, so we think people may find it useful.
It requires a browser that supports the Google Earth API, which, as far as we know is only Firefox. So, you will need to open this post in Firefox, and click ‘Activate Google Earth’ and then ‘Allow and Remember’ in the popup.
Instructions
To begin, zoom in to the location where you want to create the animation. Then click ‘Get dates’. The tool will obtain the list of dates available for that location. Note that for locations with a large number of images, this may take a bit of time.
For most animations, you will want to start the animation at a specific point in time. Go to the date you wish to start at in the Google Earth plugin, then click ‘Set first date’. This will exclude all dates before this date.
Now go through each image deciding whether to include it in your animation or not. You can either select images with the plugin or use the ‘Next’ button to cycle through images. If you definitely want an image, click ‘Include date’, if you definitely do not want an image, click ‘Exclude date’. The tool has two modes. You can choose to select specific dates to include in your animation, or select specific dates to exclude. If you are only removing a few images, then the latter mode is easier.
Once you have gone through the imagery you can see how it will look by clicking the ‘Play’ button. If you are satisfied with the results, set speed of the animation by adjusting ‘Step’ which is the time between frames, then click ‘Download Tour’. You can now open the downloaded file in Google Earth and play the tour.
loop. Step (milliseconds):
Use ‘includes’ only
Use ‘includes’ and ‘dates available’
| Included dates | Dates available | Excluded dates |
|---|---|---|
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