On 08/28/2008 12:04 PM, Torsten Dreyer wrote:
> Here is a little patch that changes the behaviour of the VOR CDI and OFF-flag 
> for indicators like the HSI when getting outside the range of the VOR 
> station.

....

> The benefit is:

> - No more jitter for flag and needles

That's not a benefit.  The real instrument exhibits flicker when marginally
out of range.  Getting rid of the flicker is a Bad Idea.

> - Ability to animate the OFF-Flag with a smooth transition.

That's not very important, far less important than getting the previous
item right.  In many situations, the real flag exhibits a fast transition,
faster than the blink of an eye.

> - CDI and GS needle deflection shows correct values when in range 

That's not new.  That should go without saying.

> and show some wrong indication when the range is 
> exceeded

Pilots don't like it when instruments "show some wrong indication",
particularly when the flag is not clearly in the OFF state.  Wrong
GS indications can be fatal.

> - CDI and GS needle start to move, even when the OFF flag is visible

OK, but there are better ways to achieve this.

============

The existing model of random flicker is _mostly_ a good idea, albeit 
imperfectly implemented.  The real instrument exhibits flicker.  

  1) Slowing down the model's rate of flicker would be an improvement in 
realism.  Right now it flickers at frame rate, whereas a coherence time 
on the order of a tenth of a second would be more realistic and more 
esthetically attractive.  The patch to do this is vastly simpler *and* 
results in vastly more realism than trying to get rid of the flicker entirely.

  2) Putting a time-based (not position-based) low-pass filter on the
needle motion would be a good idea for multiple reasons, even when in 
range.  This by itself would remove almost all of the esthetic objections 
to the flicker model.

  3) Flag flicker by itself is much less of a problem, but if you really 
want smooth animation of the flag, again a time-based low-pass filter does
the job.  It should be asymmetric (fast-OFF, slow-ON).

Also note that many instruments do *not* just attenuate the GS signal 
toward zero when out of range;  for very good reasons they drive the 
needle to a full fly-up indication when out of range.  

  Yes, there are some old, dumb instruments that do park the needle at
  zero, but it is a Bad Idea to assume that all instruments are old and
  dumb.

Code to allow the instrument designer to implement whichever "parking" 
behavior is desired -- dumb or smart -- has been in the _Sport Model_ 
for years.


-------------------------------------------------------------------------
This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
Build the coolest Linux based applications with Moblin SDK & win great prizes
Grand prize is a trip for two to an Open Source event anywhere in the world
http://moblin-contest.org/redirect.php?banner_id=100&url=/
_______________________________________________
Flightgear-devel mailing list
Flightgear-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/flightgear-devel

Reply via email to