The iPhone has an internal compass, apart from the AGPS. http://theiphonewiki.com/wiki/index.php?title=Compass
The text you found describes how to obtain a pseudo-compass heading. /Mogens On 12-05-2011 12:43, Thoern wrote:
Aha I found a page that seems to explain the iphone compass "Given that we know our position, in latitude and longitude, it's possible to calculate this Magnetic Declination. It can vary from 0 to 30 degrees here in North America. So, knowing the direction that a magnetic compass points to, there is a calculation that tells you the offset, East or West, and the angle to correct, to obtain True Geographic North. " http://www.ipodobserver.com/ipo/article/exploring_the_compass_app_in_the_iphone_3gs1/
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