On 05/14/2018 12:59 AM, Glenn W wrote:
> Hi,
> 
> I'm trying to model atmospheric refraction on a globe. My first attempt at this
> was to have a sphere centred at the origin representing the earth surface, and
> then several concentric spheres that represent the different densities (and
> therefore different refractive indices) of air as you gain in altitude:
> 

I'm not aware of anyone having modeled this effect in POV-Ray. Some 
thinking aloud - and without morning coffee as yet...

When your camera is inside an object you want to use the keyword 
'hollow' or 'hollow on'. When a ray starts, the containing interior is 
associated by where the ray origin sits. I'm not sure what happens when 
there are multiple initial surrounding interiors. Which does it pick... 
Is the ordering stable...

My understanding is when a ray leaves a surface it drops an interior and 
moves to the previous enclosing interior as determined when it 
encountered starting surfaces / interiors - or it drops back to no 
interior. So maybe shells, but always 'above' the camera with the most 
dense shell the most inside? Top surfaces mattering geometrically and 
the bottom surfaces compressed..?

Others here know atmosphere better than me, but atmospheric refraction 
is a continuous effect as the density increases toward the surface so 
the real light path will be a curve. If you want to demonstrate that 
curvature somewhat precisely your probably out of luck - too many 
surfaces(1) to approximate anything appearing continuous. If all you 
want is to demonstrate the visual offset for some point(s) at a distance 
from some set altitude perhaps a single containing sphere with some 
mathematical adjustments for an effective delta-IOR is enough?

It might be for near-ish objects like a mountain range in the distance 
you'll not have the accuracy in POV-Ray you need at realistic IORs to be 
able to 'see' the effect.

Expect near-ish atmospheric effects would be dominated by heat / 
convection currents, particles, humidity etc more than atmospheric 
density.

Bill P.

(1) - Perhaps there is some way to distort the surface of the containing 
objects(s) in a way which would equivalently and continuously model the 
effect?

Post a reply to this message