At 11/13/02, you wrote:
JD Fenech writes:

 > Major note: I've been trying to follow FG development for somewhat
 > over a year, and still haven't been able to really figure out how FDMs
 > are handled (are they internal to the software, or are they externally
 > loaded).

The FDMs are the aerodynamic engines (special-use physics engines).
Unlike most simulators, FlightGear contains several different
aerodynamic engines: JSBSim (the default), YASim, LaRCsim, UIUC (based
on LaRCsim), and a few other special-use ones.

The three major FDMs are runtime-configurable using external files so
that they can simulate the physics of many different aircraft types:

- JSBSim uses XML files scattered throughout $FG_ROOT/Aircraft/
- YASim uses XML files stored under $FG_ROOT/Aircraft-yasim/
- UIUC uses INI-like files stored under $FG_ROOT/Aircraft-uiuc/
The Aircraft-uiuc dir is for the most part obsolete, but the files still run (the code is backward compatible). The $FG_ROOT/Aircraft/UIUC supercedes it.


Before you say anything, yes, I agree that this is wrong.  We either
want something like

  $FG_ROOT/Aircraft/fdms/jsbsim/c172r.xml
  $FG_ROOT/Aircraft/fdms/yasim/c172r.xml
  $FG_ROOT/Aircraft/fdms/uiuc/c172r.dat
- I like this approach ("fdm/type" named dirs vs "aircraft/aero" below). There's a lot more than just aero in the aircraft files: inits + aero + gear + engine + flag setting, etc. Also, I think from a developer standpoint, it's best to start w/ the fdm-type/aircraft-name rather than aircraft-name/fdm-type.

- Note that once in the fdms/*/ dir, the aircraft will each need their own dir like I have in $FG_ROOT/Aircraft/UIUC/ because, for instance, we could have upwards of 60 or so aero data files.

- My guess is that JSBSim will also be using supporting aero data files, so I suspect it will also need a special dir for each aircraft.

Regards,
Michael

or something like

  $FG_ROOT/Aircraft/c172r/aero/jsbsim.xml
  $FG_ROOT/Aircraft/c172r/aero/yasim.xml
  $FG_ROOT/Aircraft/c172r/aero/uiuc.xml

depending on whether we want to group the aero files together with
others using the same FDM or together with others for the same
aircraft type.  We could even replace 'aero' with 'physics' to make it
clear to new users what's going on, since physics engines are starting
to be heavily used in the 3D gaming world.

 > "The modern definition of 'racist' is someone who is winning an
 > argument with a liberal."
 >
 >  --Peter Brimelow

What's the modern definition of 'liberal'?


All the best,


David

--
David Megginson, [EMAIL PROTECTED], http://www.megginson.com/

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 Prof. Michael S. Selig
 Dept. of Aero/Astro Engineering
 University of Illinois at Urbana-Champaign
 306 Talbot Laboratory
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 (217) 244-5757 (o), (509) 691-1373 (fax)
 mailto:m-selig@;uiuc.edu
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 http://www.uiuc.edu/ph/www/m-selig/faq.html (FAQ)
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