Re: [Flightgear-devel] Dots, degrees and magic '5's

[James T. <zak...@ma...>]

On 3 Jan 2009, at 17:38, John Denker wrote:

>
>  A) We are now agreed that deflection as a fraction
> of full scale is a supported feature, not deprecated,
> not scheduled to "rot", right?

Err, I would say that we don't have that as a current feature, but I  
think that's getting into semantics of what 'normalised' means, and my  
opinion as a graphics coder may be different to an engineering  
meaning. Anyway, there is certainly no way (even if it was desired) of  
getting rid of heading-deflection or gs-deflection, and they have to  
continue to work.

>  B) The proposal is to add a new output, just like
> the old output, but with a different normalization
> factor.  That's the main point of this thread, right?

At this point, I think so. There's code that would be simpler if it  
could talk about degrees deviation rather than peg-to-peg percentage  
(eg, all the autopilots that 'capture with 0.5 degrees (or whatever)'  
of the localiser) but I think a degree based definition will always be  
troublesome. Clearly real world autopilots know about a signal from  
the navradio, not real degrees, so when the manual specifies a value  
in degrees they're applying some approximate conversion factor.

>  C) The old oddly-normalized output will continue to
> be supported for the foreseeable future, since is doesn't
> interfere with new features and preserves compatible
> interoperation with older CDIs, right?

Yep, sadly that's too far baked in to be removed at this point, at  
least for the amount of effort required.

>  D) Lesser points include:
>
> -- Outputs should not be clamped by the tuner.  Each
>  CDI head may choose to peg the needles, or not, in
>  its own way.

Yep, but someone needs to verify what the fallout of such a change  
might be.

> -- Localizer sensitivity is runway-dependent.
>
> -- Dozens of other navradio.cxx bugs as discussed
>  elsewhere.

Indeed, but again not the core thing I'm worrying about here.

James