When you lay the iPhone 3GS flat, Nearest Tube shows pointers to all the London Tube lines, colour-coded to match the line.
There are already several AR apps available for Android, such as the Crave fave Google Skymap. But our resident Android addict, Ian, was impressed by the smoothness of Nearest Tube as we panned around the scene, compared to the Android AR apps we've tried.
Nearest Tube uses images from the iPhone's camera, rather than a live video feed. That means we occasionally saw the square focus target that the camera uses, although we couldn't tap to focus on anything within the app. It also means it can't manipulate or analyse the image, so the pointers are positioned using only GPS and the compass, instead of recognising any visible landmarks or tags on billboards, for example.
While this works well for a Tube station app, Acrossair told us it's a major problem when trying to create AR apps that are linked more tightly with the real world. It pointed us to an open letter to Apple, signed by 14 software development companies and researchers, who are begging Apple to open its video camera API in the same way Android does, along with videos showing prototypes of the cool stuff that could be just around the corner for AR.
With access to the video stream, developers can do things such as recognise historic buildings and display tourist info, or clock a movie poster to overlay a streaming video trailer of the film. Developers are already working on prototypes using private APIs that Apple won't approve in the App Store, and they want Apple to release a public API that will make their applications App Store friendly.
We'll be taking some of the Android AR apps for a spin on the HTC Magic soon, so stay tuned for a test-drive on the current king of AR action.