Martin van Beilen wrote:
> I think I am beginning to understand what the source of the
> confusion is. As most of you know, weather reports specify the winds
> as a _from_ heading. However, in simulated space I tend to think of
> wind as a vector, i.e. a _to_ heading. Apparently, two out of three
> FDM's agree with my point of view. So what is the consensus on this
> one? To or from?
>
> Tony Peden wrote:
> > From is the accepted convention in aviation, hopefully that's what
> > JSBSim treats as positive. I'll attempt to verify later.
I took my hint from the naming of the accessor functions:
FGInterface::get_V_{north|east|down}_airmass();
These imply pretty strongly that they return the velocity of the
airmass, in the (horrifically ugly but well-understood) "local"
coordinate system. That is a "to" vector, by definition. Really, the
"from" convention applies to a 1-dimensional compass direction; I'm
not aware of anyone else trying to apply it to a 3D vector
environment.
That being said, I'd be happy to negate my wind vector if that's what
folks decide.
> I also found an interesting glitch with YASim: the airspeed
> indicator displays the ground speed. I thought I was going to stall,
> but didn't. :)
Yup, so it does. That's a problem. I'm setting the output stuff in
FGInterface wrong, somehow. Ah, found it: in YASim.cxx, you'll note
that I call set_V_rel_wind(); try to find out where the wind gets
added in. Oops.
I need to remember where I keep the wind and what conventions are used
to fix this, but need more urgently to go to bed. I'll have this
fixed tomorrow.
Andy
--
Andrew J. Ross NextBus Information Systems
Senior Software Engineer Emeryville, CA
[EMAIL PROTECTED] http://www.nextbus.com
"Men go crazy in conflagrations. They only get better one by one."
- Sting (misquoted)
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