On 9 Sep 2009, at 21:47, Torsten Dreyer wrote:
> I don't think clamping the deviation to +/-0.7 degrees and the
> normalized
> value to +/- 1.0 is a good idea. Instruments like the KI525 HSI move
> the
> glide slope needle out of sight when the glideslope signal is not
> valid or
> you are way above or below glideslope.
> If you clamp the values, this information is lost for the instrument.
This is a fair point - the problem is it's a situation the current
property also handles incorrectly - it acts as if the sensing area for
the GS is much 'thicker' than it actually is - so rather than
reporting invalid, we just report extremely large 'valid' values. What
needs to happen is to communicate the absence of a valid GS signal
(for whatever reason) some meaningful way.
(This, btw, is why the Mk-VIII has the -ncd flags for each input/
output property)
The two solutions I can think of:
- use -9999 (or similar) to indicate an invalid signal OR
- use the (existing) has-gs flag to indicate it (or a new flag, like
gs-valid)
The second seems much more sensible to me, in terms of minimal changes
to existing instruments. Note that right now, the has-gs flag is not
quite useful for this purpose, because we don't update it based on
radio reception - I'd need to audit current users to see if it could
be modified that way, or whether a new property is safer.
(the first solution needs special handling by every existing
instrument and script, I think, though it is a method used elsewhere
in the code)
In practice, all the instruments I've seen so far handle 'parking' the
GS needle in two ways: either masking layer above the needle, at the
extremities of the range, or an interpolation table where the extreme
values map to a particular hidden position. Also, all the instruments
I've changed so far have implemented a clamp themselves, either via an
interpolation table, or min/max values on the animation element - I'm
not creating any 'new' clamping, that I've seen so far.
So, I think clamping is correct (and matches what we do for the
heading needle) - what's needed is a flag property, and for panel /
instrument authors to use that flag to implement a parking behaviour
if they wish.
Regards,
James
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