Getting started with AR on the iPhone: How to position things?

Just starting to play with Augmented Reality on the iPhone ... and I have some questions:

1. How do you position elements on the screen? I assume that it is based on a given longitude, latitude a开发者_StackOverflownd altitude (but I could be wrong)???

2. Any solid resources, tutorials, etc... dedicated to building AR type apps for iOS?

Thanks much

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http://www.jonathansaggau.com/blog/2010/10/iphone_ipad_devcon_sample_code.html

This is a talk with sample code. If you understand atan, sin, cos, you are halfway there.