Derivation of DSO brightness versus distance in FT1.2

[t00fri]

Well I thought some of you might be interested in the way the galaxy brightness is implemented as function of the observer distance from the galaxy border in the forthcoming Celestia-1.4.0pre-FT1.2. It also incorporates the smooth day-night blending that FT1.1 was still lacking.

Here is the extensively commented PDF file of the Maple worksheet that I used to derive the resulting behaviour. You can also look at the plots if you are not interested in the mathematics.

Derivation of DSO brightness versus observer distance in FT1.2

Of course you need a standard PDF plugin in your browser...

Bye Fridger

[Boux]

Well, I am a bit rusted on the math side but your great work demonstrates again that Celestia is not simply a toy but something really serious built on a real, rational, scientific approach.
Kudoos

[Vincent]

It also incorporates the smooth day-night blending that FT1.1 was still lacking.

I've been waiting for a new day-night blending function for monthes, so this is very good news Fridger. Thanks !
Can you also provide explanation about the new day-night blending function ?

[t00fri]

It also incorporates the smooth day-night blending that FT1.1 was still lacking.

I've been waiting for a new day-night blending function for monthes, so this is very good news Fridger. Thanks !
Can you also provide explanation about the new day-night blending function ?

Yes, certainly. But I have little time right now.

Are you interested in how this works in the code or more what the background for the blending function is? Or what?

In short: suppose at night you start with a certain value of 'faintestMag' ~7 - 11, say. If you are on a planet with an atmosphere, the values of 'faintestMag' and 'saturationMag' are smoothly /decreased/ for increasing sky-illumination via an atmosphere. This mechanism is already present in Celestia.

So all you got to do is to implement some function(faintestMag) that drives the brightness of the object to be rendered to values <=0 when daylight comes on. How this works for my brightness profile, you may see in my second plot.

Bye Fridger

[Vincent]

Ok, thanks for this short - but effective - explanation Fridger.
Is this new function going to modify also the rendering of the day-night limit area as seen from space ? My question was more precisely -not enough, apparently - about the earth illumination algorithm.