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True altitude can be acquired from GPS information but it has about 1 order of maginitude (on average) less accuracy than the horizontal accuracy. (i.e. If your horizontal accuracy is plus or minus 5ft your vertical accuracy could be plus or minus 50ft.) All that being said, I would reccomend checking the aviation apps. They may have something. It all depends on if the core location part of the SDK allows you to acquire the vertical information from the sattelites. Hope this helps.