I'm trying to create kind of a crescent-shaped island and I'm using an
isosurface to do it, but I've run into kind of a strange problem: if I
increase the size of the containing sphere, the top half of the iso
disappears. Thing is, I don't know if this is a bug or an oversight on
my part.. so I'm posting it here in .general instead of
povray.unofficial.mac.bugreports.unconfirmed.etcetcetc or something of
the sort.

Using MacMegaPOV 0.7 (the problem appears in both classic and carbon
versions). Short test code follows:

#version unofficial MegaPov 0.7;
	
camera { location <0, 6, -10> look_at <0, 0, 0> }

light_source { <-2, 10, -3> rgb 1 }
	
#declare test = function { pigment { wrinkles scale .5 } }
#declare test2 = function { pigment { wrinkles scale .5 translate <100,
100, 100> } }
	
isosurface {
	function { (x^2 + y*10 + z^2) + .5^(((x*3)+.75)^2 + ((y-0)*10)^2 +
((z*3)+.75)^2 + test2 - 1) + 2*test - 1.8 }
	threshold 0
	eval
	contained_by { sphere { <0, 0, 0>, 1 } } // Change this to a higher
number to see the problem.
	pigment { color rgb .5 }
	finish { ambient .5 }
	scale 5
	}
	
plane { y, 0 pigment { color rgbf <1, .5, .5, 1> } }

Can anyone reproduce this, or figure out what I'm doing wrong?

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Xplo Eristotle wrote:

> I'm trying to create kind of a crescent-shaped island and I'm using an
> isosurface to do it, but I've run into kind of a strange problem: if I
> increase the size of the containing sphere, the top half of the iso
> disappears. Thing is, I don't know if this is a bug or an oversight on
> my part..

(cutting and pasting from a recent post...)
This is very probably a max_gradient problem. It has driven many people
mad before (including me). The trick is to give a proper max_gradient
value instead of relying on eval. A detailed explanation can be found here
:
http://www.econym.demon.co.uk/isotut/keywords.htm

G.
--

**********************
http://www.oyonale.com
**********************
Graphic experiments
Pov-ray gallery

Post a reply to this message

Gilles Tran wrote:
> 
> Xplo Eristotle wrote:
> 
> > I'm trying to create kind of a crescent-shaped island and I'm using an
> > isosurface to do it, but I've run into kind of a strange problem: if I
> > increase the size of the containing sphere, the top half of the iso
> > disappears. Thing is, I don't know if this is a bug or an oversight on
> > my part..
> 
> (cutting and pasting from a recent post...)
> This is very probably a max_gradient problem. It has driven many people
> mad before (including me). The trick is to give a proper max_gradient
> value instead of relying on eval.

Damn you, max_gradient! DAMN YOU TO HELL!!

*cough*

Er, I mean, thanks a lot, I'll be sure to look into it.

-Xplo

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