On 03/01/2007 08:02 PM, Dave Perry wrote:
> .... there are only 3 options still being put forward; all having to
> do with how the kap140 gets the baro shift. These are:
>
> 1) computes it in kap140.nas using the pressureToHeight()
> function already there but not presently used (need to check the
> constants for consistency with John's model),
>
> 2) gets the kollsman shift value already computed by John's
> altimeter.cxx (but not presently saved to the property tree by
> John's altimeter.cxx) , or
>
> 3) gets it by fetching from the encoder propeties the indicated
> altitude and the pressure altitude, and then subtracting.
I would add
4) Use the shift() function from the Kollsman object in
http://www.av8n.com/fly/fgfs/atmo.nas
The comparison as I see it goes like this:
1 2 3 4
verisimilitude + 0 0 +
simplicity + 0 0 +
accuracy + + + +
computational 0 + + +
efficiency
It seems like option (4) is Pareto-superior. As I said previously,
I would be astonished if real autopilots didn't use this approach,
or something very similar.
===================================
In the last couple of days, there have been bugfixes and
upgrades to atmo.nas, atmo.hxx and atmo.cxx ... the current
versions are, as usual, obtainable from:
http://www.av8n.com/fly/fgfs/atmo.nas
and
http://www.av8n.com/fly/fgfs/atmo.diff
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