Tuesday, March 10, 2009

Regions: Hunting Moby Dick

So I've talked before about the regions feature, it can be used to hide content until a user flies in closely. This is clever but not if there isn't a visual signal that the hidden content exists while the user is at altitude.

Open the Ocean layer in the layers panel of Google Earth 5.0 and click oceans. A mass of content will open and if you fly somewhere like Hawaii you will see an image on screen like this:

Lots of content is visible which is good. Fly out and to deal with all the placemarks crowding the view, the regions feature kicks in and you will see content disappearing. This creates the hidden treasure problem, I don't know anything is there until I fly in to see it. This isn't too much of an issue if I just want to see what is in Hawaii as I'll probably fly close to take a look but what if I want to see what is in a particular sublayer of Oceans?

A Sublayer Hidden at Altitude: Say I want to see what the BBC layer oceans layer has in it around the whole world. If I turn it on whilst I'm at high altitude (on my system, at 5,000km), leaving all the other layers off, nothing will appear. The novice user will be flummoxed, 'something isn't working' he'll think to himself, he'll probably give it a couple more on/off clicks just to check then give up in disgust. In this case the hidden treasure problem has become vital and ironically, the regions feature isn't serving any useful purpose as crowding isn't any issue with only one sublayer visible.

The Solution: A square buffer polygon (i.e. four points to calculate and render), semi transparent and filled, around any placemark content of any layer selected whilst the regions feature is hiding content. Where the squares overlap, the polygons for each placemark coalesce which cuts down rendering time. With only one sublayer visible you could just turn off the regions feature of course but I suspect this would be more difficult to implement.

In a sister post to this one also posted today I follow up with a great example of dealing with similar scale issues.

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