What's a robust strategy for displaying 3D map data for navigation?

Question

3D map data, specifically the kind you see on GPS units, or more recently on smart phones, almost always features a 'HUD' like view, which I'm trying to implement in an application of mine. I have OpenStreetMaps data (offline) available to my application, where all the geometry is specified in latitude and longitude.

With 2D maps, there's a 'standard', where almost everyone uses N*N tiles of Mercator projected data. But with 3D data,

• I don't know what projection I should be using (I still have to map the latitude, longitude and altitude to x,y,z)

• I'm not too sure what's the best way to make data continually available in 'chunks' to a display engine as a user pans and zooms the map view

If it matters, I'm using C++ with the OpenSceneGraph library (which is basically a scene graph wrapper/toolkit for OpenGL). I'd appreciate any advice!

Answer 1

It depends on what kind of navigation you're talking about. I'll assume car navigation.

Since you're only showing a small slice of Earth (as opposed to Google Earth, which can show the whole Earth), you can simplify some things, for example:

• You can convert OSM's lat/lon coordinates into localized "flat Earth" coordinates (using the latitude to calculate the ratio to the longitude).
• Projection: the perspective projection, I guess. I'm sure you'll be using a 3D engine, so you get that in the box.
• Also take a look at level of detail algorithms and data structures. If you really serious about your project, I recommend buying Level of Detail for 3D Graphics book
• There are several open source OSM 3D projects, so you can study their code and contact developers: http://www.osm-3d.org/map.htm, http://wiki.openstreetmap.org/wiki/3D_Development

Good luck!