alphaQuad nous apporta ses lumieres en ce 2007/10/10 17:30:
> 
> Why does Mike say this is the function for a gravity well?
> x*x - 0.002/y*y + z*z
> 
> Or more importantly what must be done that I am not doing to render a
> surface as Mike has here:
> http://www.econym.demon.co.uk/isotut/more.htm
> 
>

Gravity is a function of the sum of the mass involved divided by the square of 
the distance. g = (M1 + M2)/R^2
The gravity well is the 4D deformation of space due to the gravity of any 
object. The resulting 4D shape is then projected into 3D space in the form of a 
bent surface, the 3D space been flatened to 2D and the 4D deformation flatened 
in 3D. The proposed function is the end result of that projection.

The -0.002 is an arbitrary ponderation factor.

The proposed shape is for a punctual mass, whitch is an acceptable 
simplification in most cases and the actual situation in the case of a black hole.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you downloaded and printed the 
Renderman Interface documentation, so you'd have a little light reading to take 
on holiday.
Alex McLeod a.k.a. Giant Robot Messiah

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