Last week we looked at animating historical imagery by using Google Earth Tours. While looking around in historical imagery we discovered an interesting effect: the historical imagery is not correctly synced to the timeline when Google Earth is zoomed out.
Last year we had a look at a number of situations in which Google Earth shows different imagery depending on the zoom level. The effect we are looking at today is similar in that the zoom level has an effect on what you see, but we think today’s effect is more of a bug or error, whereas the effects we have looked at in the past actually enhance Google Earth, as they provide access to extra imagery.
To see for yourself what we are talking about, load this KML file in Google Earth. It should switch to historical imagery, change the date to November 1st, 2002 and centre the view over Europe. Zoom out as far as you can and then slowly zoom in. As you zoom in you should notice patches of images appearing in several stages.
The same place at slightly different zoom levels without adjusting the time slider.
If you look carefully at the two screen shots above, there are more patches of imagery in the right hand image even though the only change made was to zoom in a little. Interestingly, if you zoom out until those patches disappear, then move the time slider forward a bit to 2003, the missing patches do appear.
As far as we can tell, the zoomed in imagery more accurately reflects the correct timeline, i.e., all images shown when zoomed in are dated on or before the date shown on the timeline.
We also found some cases of imagery that were not correctly synced to the time-slider at any zoom level. For example, there is a patch of aerial imagery in France dated January 1st 2002 that doesn’t show until the time-slider reaches December 2002. Being aerial imagery the date is only approximate and probably only means the imagery was captured some time during 2002, so it is possible the imagery is stored in the database with a date range and Google Earth only shows it when the upper bound is reached. Find the imagery we are talking about with this KML file .
Overall, we don’t think it is a major problem, but do keep in mind when searching for imagery of specific dates that you should zoom in as far as possible for greater accuracy and double check the actual dates of imagery rather than relying solely on the timeline.