On 2021-09-21 2:27 AM (-4), Thomas de Groot wrote:
> 
> Yes? However, now I would like to see a combination of both: hills (4th)
> with haze (3rd). I am effectively missing a (bluish) distant haze in the
> 4th generation hills, which, you certainly have observed. Similarly, in
> France, when visiting the Vosges region, one speaks of "La ligne bleue
> des Vosges" i.e. "the blue line (or silhouette) of the Vosges".

Yes, I have indeed noticed that.  Sky is something I've been struggling
a long time to get right, and this certainly isn't the final form.  I
have a lot to learn about what colors the sky.  There is a blue haze in
the 4th generation image, but it is subtle.  I used just enough ground
fog to reproduce the brightness gradient I see in photos, but this
doesn't seem to translate well to extinction.  I wonder if this is
because POV-Ray's ground fog is flat, while the Earth is not.  There is
also turbidity to be considered.

The color of the haze also varies depending on what's in the air.  In
the Caribbean, it is whitish when Sahara dust crosses the Atlantic.  In
the northeastern USA, the haze is brownish, I presume due to nitrogen
oxides.

I see media in a future implementation, but it is currently low priority.

Attached are 1st and 4th generation scenes.  I wrote the first
generation render rig in 2003 withing a month of downloading POV-Ray,
and as you can see, the sky is just a plain background.  The 4th
generation scene has the hills maxed out at 5000 meters, and I
implemented the rig so that higher elevation caps push the hills
proportionately further into the background.  It's been a few years
since I wrote the code, but I estimate the hills are on the order of 20
km away from the camera.

A 2nd generation scene is not shown, because it did not provide an
automatic sky.

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