Augmented Reality - Using only GPS

Question

I'm planning on doing an AR application that will just use GPS technology to get a location, and then use compass/gyroscope for tracking 6DOF viewfinder movements. Its a personal project for my own development, but I'm looking for starting places as its a new field to me so this might be a slightly open ended question with more than 1 right answer. By using GPS I am hoping to simply the development for my first AR application at the cost of its accuracy.

The idea for this AR is not to use any vision processing (relying on GPS only), and to display 3d models on the screen at roughly correct distances (up to a point) from where the user is standing. It sounds simple given games work in a 3D world with a view point and locations of faces/objects/models etc to draw. My target platform will be mobile devices & tablets potentially running one of these OS's WM6, Phone7 or Android.

Most of the applications I have seen use markers and use AR-ToolKit or ARTag, and those that use GPS tend to just display a point of interest or a flat box on a screen to state your at a desired location.

I've done some very limited work with 3D graphics programming, but are there any libraries that you think may be able to get me started on this, rather than building everything from the bottom up. Ignoring the low accuracy of GPS (in regards to AR) I will have a defined point in a 3D space (constantly moving due to GPS fix), and then a defined point in which to render a 3D model in the same 3D space.

I've seen some examples of applications which are similar but nothing which I can expand on, so can anyone suggest places to start of libraries to use that might be suitable for my project.

Answer 1

Sensor-based AR is do-able from scratch without using any libraries. All you're doing is estimating your camera's position in 6DOF using, and then performing a perspective projection which projects the known 3D point onto your camera's focal plane. You define your camera matrix using sensors and GPS, and perform the projection on each new camera frame. If you get this up and running that's plenty sufficient to begin projecting billboards, images etc into the camera frame.

Once you have a pin-hole camera model working you can try to compensate for your camera's wide-angle lens, for lens distortion etc.

For calculating relative distances there's the haversine forumula.

Moving to 3D models will probably be the most difficult part. It can be tricky to introduce camera frames into OpenGL on mobile devices. I don't have any experience on windows mobile or android, so I can't help there.

In any case have fun, it's really nice to see your virtual elements in the world for the first time!