Re: [Flightgear-devel] Altitude above ground

[Mathias <Mat...@gm...>]

On Tuesday 31 July 2007, Eser KUBALI wrote:
> Before my question, I want to say hello to all flightgear developers. I'm
> new to Flightgear ( nearly 3 months) and also to Linux. The open-source
> concept is a wonderful way to develop something especially FlightGear. Now,
> I'm trying to write my own FDM. It works fine for me but I have some
> problems.
>     These days, I work on calculation of altitude above ground level value.
> I couldn't transfer JSBSIM or YASIM get_agl functions into my FDM. Then,
> I decided to use get_agl functions in flight.cxx . But, I couldn't
> understand the usage of it. I don't know the variables like normal[3] or
> pt[3].
>    Can you help me about the get_agl functions? Thank you!

Inputs and outputs are vectors in the cartesian earth fixed coordinate system. 
That is the one with the origin in the earths center the x axis towards 
lat=lon=0 the y axis towards asia and te z axis towards the north pole.

The ground queries from within FGInterface are only valid when you set up a 
small query cache using the prepare_ground_cache function. Then you can ask 
that cache for agl values from within that sphere you used in the prepare 
call.

     Greetings

           Mathias