In article <40784f64@news.povray.org>, Micha Riser <mri### [at] gmxnet> 
wrote:

> Principally it is very simple:
> Given the isosurface function f: (x,y,z) -> R, put in the ray equation r: t
> -> x0 + t* v0, i.e. f(r(t)) which is a 1dimensional function t -> R. Now if
> the surface is at f(x,y,z)=0 all you have to do is to find the roots of the
> function, i.e. the smallest t for which f(r(t))=0. POV-Ray does this with
> the constant slope method starting from the first intersection with the
> container. The used slope is the max gradient.

I think you are mistaken, unless you mean something by "constant slope 
method" other than what I think you do (something like Newton's method 
with a constant "derivative", using the function value and max gradient 
to estimate the minimum possible distance to a root). POV uses a 
variation of the bisection algorithm, using the maximum gradient to 
decide if it is possible for a root to exist in an interval. The 
starting interval is defined by the first and last hits of the container.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

Post a reply to this message