Re: [Flightgear-devel] Moonlight

[Thorsten R. <tho...@sc...>]

> Well, it's the moon's power spectrum passed through the luminosity
> function [1] and summed.  So the luminosity function takes the
> biophysics of the human eye into account.

Well, my argument started with:

"The reasoning is that taking the log of the light flux introduces a
perception model."

To which you objected, to now replace 'perception' by 'physics of the  
human eye'.

So can we finally agree that the biophysics of the human eye has to do  
more with _perception_ of light rather than the physical properties of  
light? And that this statement is independent on whether Biophysics is  
real physics or not?

I grant you that there's real physics to how the eye works (even if we  
don't know it at the level of Quantum Electrodynamics), how a camera works  
or how photographic emulsions work - but it still makes conceptually sense  
to separate the physics of light emission from that of light propagation  
and detection - because while e.g. wavelength is a statement about how  
light is, lux is more a statement about how the eye is.

> In any
> case, I still don't see why the simple log(lux) calculation could not
> be part of the simgear ephemeris code as it currently is.

Conceptually because modeling the physics of the human eye is something I  
would not expect to find in an ephemeris code as it has little to do with  
orbital mechanics. Whereas a moon phase has a lot to do with orbital  
mechanics.

> "I've seen..." is a rather vague and non-reproducible bug description.

I've written before that it's basically always wrong - it doesn't matter  
where and when you start up. Giving you a precise set of conditions would  
imply that it has anything to do with these conditions - which it has not.

Start at any time you like, any date you like, any location you like -  
compare the zenith angle written by the code with the visual position of  
the moon in the sky (you might have to not render the terrain if the moon  
is below the horizon) - find that they're inconsistent.

(Of course that comparison works best if the moon is at the horizon, the  
zenith or the nadir because that makes measuring the zenith angle of the  
rendered moon disc easiest).

* Thorsten