Hello everyone,

I'm currently playing with the isosurface and f_spiral function, and I'm
experiencing 2 curious artifacts.
I hope someone could point me in the right direction to solve this.

Image: http://ronkhar.fr/Informatique/3D/Povray_isosurface/ten_spirals.png

Problem 1: There is something like a dark sphere at the origin of the spirals
(in fact, there are ten of these spheres at the same position, 5 red and 5 black
each one created by a spiral)

Here is a smaller version of the code I wrote (1 spiral only) :
============================================================
#version 3.7;
global_settings { assumed_gamma 1 }
#include "colors.inc"
#include "transforms.inc"

light_source { <-1,8,2> color White}

camera {
location <0,4,0>
look_at  <0,0,0>
}

plane {y, 0 pigment { checker Grey, White }}

isosurface{ function{f_spiral(
   x,y,z,
   6,   // distance between windings,
   0.2, // thickness,
   2,    // outer diameter of the spiral,
   0,0,  // not used,
   0
   )}
   accuracy 0.01
   threshold 0 // default value
   max_gradient 37 // high value = more precision = more render time (ideal
value indicated in "messages")
   contained_by{sphere{<0,0,0>,15}}
   texture{pigment{ color Red filter 1 }}
   }
============================================================
Image obtained:
http://ronkhar.fr/Informatique/3D/Povray_isosurface/one_spiral.png

Problem 2: Near the center, the exterior part of the spirals end with a straight
line, where I was expecting the curve to continue.

To help see the lines, I hid the central dark sphere inside a slightly bigger
white sphere
sphere{<0,-0,0>,r1 texture{pigment{ color White }}})

Here is the result:
http://ronkhar.fr/Informatique/3D/Povray_isosurface/ten_spirals_zoom_lines.png

Are these bugs, features or something wrong in my code?
Does anyone know how I could fix it?
Thanks in advance,

Ronkhar

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