Re: [Flightgear-devel] Coordinate Systems

[<js...@ha...>]

> The simulation calculates the velocities with respect to the fixed body
> (airship) system. How can I transform this velocities in the position of the
> FlightGear
> Scenery. I tried several transformations, but it's not working. How did you
> do it? As far as I understand the simulations "LaRCsim"
> works also in the body fixed system and has to transform the velocites
> (integration) into coordinates of the FlightGear-System.

This is one reason why I suggested you consider working with us to add this 
capability into JSBSim, rather than create another bunch of redundant code.

Anyhow, we use quaternions to create a transformation matrix that takes the 
current body-axis velocities and transforms them into "world system" (or "local 
system") values. We then integrate the velocities to get change in distance 
over the integration time.

From the JSBSim code base see:

FGState.cpp
FGPosition.cpp

You can view the latest versions online at (make sure the entire URL is on one 
line):

http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/jsbsim/JSBSim/FGState.cpp?
rev=1.64&content-type=text/vnd.viewcvs-markup
http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/jsbsim/JSBSim/FGPosition.h?
rev=1.35&content-type=text/vnd.viewcvs-markup

Jon