On Mon, 2007-02-26 at 04:57 -0500, John Denker wrote:
> Here is the nasal code to calculate the Kollsman shift.
>
> # Typical usage: indicated_altitude = pressure_altitude -
> kollsman(baro_setting)
> k_ft = k_set = nil;
> kollsman = func{
> if (arg[0] == k_set) {return k_ft}
> k_set = arg[0];
> k_ft = 145442.156 * (1 - math.exp(math.ln(k_set/29.921260) *
> 0.1902632365))
> }
>
This is virtually no change. Only the constants are different (more
digits).
>
>
> 1) This achieves the goal of realism in the sense that it allows
> the autopilot code to calculate the Kollsman shift using only
> information available to a real autopilot.
>
> I'd be astonished if real-world autopilots used anything much
> different from this.
>
> 2) This is computationally efficient in the overwhelmingly-likely
> case that the baro_setting is not being changed very often.
>
> 3) If you want to standardize this across the FG fleet, put it in
> some accessible place [perhaps atmo.nas] and let people call it
> from there [as atmo.kollsman(...)] rather than cut-and-pasting
> it in multiple places.
>
> 4) If you don't think this is -- for all practical purposes -- the
> right answer, please explain what is the right answer ... and
> explain how a pilot could tell the difference between this and
> the right answer.
>
> 5) Since this has some advantages and AFAICT no disadvantages, it
> removes any temptation to use the c++ altimetry object as an oracle
> for computing the Kollsman shift.
>
So only the altimeter can compute the kollsman shift via "your oracle"?
>
> ===================================
>
> Tangentially related note: I made one recent change to the package
> of diffs:
> http://www.av8n.com/fly/fgfs/atmo.diff
>
> I rigged it up so that encoder.[ch]xx are no longer needed, and are
> not even mentioned in the Makefile.am or anywhere else. When you
> configure an <altimeter> you get an instance of the Altimeter class,
> and when you configure an <encoder> you get a different instance of
> the Altimeter class. The only difference is that the former has a
> default <quantum> of zero, while the latter has a default <quantum>
> of ten.
>
> Users should not notice any difference (except that their altimetry
> suddenly becomes much more accurate). The configuration files such
> as generic-instrumentation.xml can stay exactly the same, and the
> runtime interface (via the property tree) is upward-compatible.
>
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--
Dave Perry <[EMAIL PROTECTED]>
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