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Map Projection in the 3D Environment


Do 3D map applications use projected maps?


Why? Why flatten (project) the world if you are just going to use them in a 3D environment; isn’t that a runaround?

Yes, but necessarily.  Raster map images must first exist as a 2D map image.  These map images are then stretched over a sphere in the 3D environment.  The map tiles exists natively as a 2D graphic that is warped over the 3D surface.  Geographic data that is collected, compiled, and served up need to have some base spatial awareness/reference.

What does Local.Live 3D do?

Virtual Earth map tiles are pulled in and draped over a 3D sphere.  Since these map tiles are originally in Mercator projection (not the best projection for draping over a sphere -see the Google Earth image below), they go through a re-project warping process.  A happy result of using Virtual Earth map tiles is that you can switch between the map styles (unlike Google Earth), just like in 2D -which is pretty cool.


One quirk of the Mercator projection is that not all of the earth can be included in a single map -it’s just an artifact of the projection, I’ll explain why in a future entry.  The result is no coverage in the polar regions.  So Local.Live 3D must paint-in those polar gaps.  Here is an illustration of where those coverage gaps are:

It’s a good thing for Mercator users that not much is going on around the poles.

What does Google Earth do?

Unlike Local.Live, Google Earth does not use the map tiles you see in maps.Google.com, it streams in aerial imagery from a different source.  Since this imagery is not Mercator (maps.Google.com map tiles are Mercator), this means that Google Earth does not have coverage gaps in the poles.  But it is kind of a bummer because you can’t switch the map style to streets, like you can in 2D.

Google Earth does allow users to pull in outside map images on the fly and pin it to the 3D surface.  In order for map to line up, though, it must have a Platte Carre projection -not Mercator.  Check out the difference between these two overlays.  The one on the left is Platte Carre, the one on the right is Mercator.

What would it take to have a projection-less 3D map application?

It’s so improbable that it blows my mind, but here is what it would take:  That application would have to be comprised entirely of vector data (that means no satellite imagery -which isn’t much fun) and would exist in a holographic state where the geographic data was positioned perfectly upon a perfect model of the earth’s shape (the ultimate datum). Not likely.

John Nelson / IDV Solutions / john.nelson@idvsolutions.com



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