POV-Ray : Newsgroups : povray.newusers : Isosurface and f_spiral - bug or feature? : Isosurface and f_spiral - bug or feature? Server Time16 Apr 2024 06:14:39 EDT (-0400)
 Isosurface and f_spiral - bug or feature?
 From: Ronkhar Date: 24 Sep 2017 13:25:01 Message:
```
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"headline": "Isosurface and f_spiral - bug or feature?",
"dateCreated": "2017-09-24T17:25:01+00:00",
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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?