1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
|
<!-- This file copyright Persistence of Vision Raytracer Pty. Ltd. 2003-2004 -->
<html>
<head>
<!-- NOTE: In order to users to help find information about POV-Ray using -->
<!-- web search engines, we ask you to *not* let them index documentation -->
<!-- mirrors because effectively, when searching, users will get hundreds -->
<!-- of results containing the same information! For this reason, the two -->
<!-- meta tags below disable archiving and indexing of this page by all -->
<!-- search engines that support these meta tags. -->
<meta content="noarchive" name="robots">
<meta content="noindex" name="robots">
<meta content="no-cache" http-equiv="Pragma">
<meta content="0" http-equiv="expires">
<title>2.1.2 What is Ray-Tracing?</title>
<link href="povray35.css" rel="stylesheet" type="text/css">
</head>
<body>
<table class="NavBar" width="100%">
<tr>
<td align="left" nowrap="" valign="middle" width="32">
<a href="s_49.html"><img alt="previous" border="0" src="prev.png"></a>
</td>
<td align="left" valign="middle" width="30%">
<a href="s_49.html">2.1.1 Program Description</a>
</td>
<td align="center" valign="middle">
<strong class="NavBar">POV-Ray 3.6 for UNIX documentation</strong><br> <strong>2.1.2
What is Ray-Tracing?</strong>
</td>
<td align="right" valign="middle" width="30%">
<a href="s_51.html">2.1.3 What is POV-Ray?</a>
</td>
<td align="right" nowrap="" valign="middle" width="32">
<a href="s_51.html"><img alt="next" border="0" src="next.png"></a>
</td>
</tr>
</table>
<h3><a name="s02_01_02">2.1.2 </a>What is Ray-Tracing?</h3>
<a name="s02_01_02_i1">
<p>
Ray-tracing is a rendering technique that calculates an image of a scene by simulating the way rays of light travel
in the real world. However it does its job backwards. In the real world, rays of light are emitted from a light source
and illuminate objects. The light reflects off of the objects or passes through transparent objects. This reflected
light hits our eyes or perhaps a camera lens. Because the vast majority of rays never hit an observer, it would take
forever to trace a scene.
</p>
<p>
Ray-tracing programs like POV-Ray start with their simulated camera and trace rays backwards out into the scene.
The user specifies the location of the camera, light sources, and objects as well as the surface texture properties of
objects, their interiors (if transparent) and any atmospheric media such as fog, haze, or fire.
</p>
<p>
For every pixel in the final image one or more viewing rays are shot from the camera, into the scene to see if it
intersects with any of the objects in the scene. These "viewing rays" originate from the viewer, represented
by the camera, and pass through the viewing window (representing the final image).
</p>
<p>
Every time an object is hit, the color of the surface at that point is calculated. For this purpose rays are sent
backwards to each light source to determine the amount of light coming from the source. These "shadow rays"
are tested to tell whether the surface point lies in shadow or not. If the surface is reflective or transparent new
rays are set up and traced in order to determine the contribution of the reflected and refracted light to the final
surface color.
</p>
<p>
Special features like inter-diffuse reflection (radiosity), atmospheric effects and area lights make it necessary
to shoot a lot of additional rays into the scene for every pixel.
</p>
<br>
<table class="NavBar" width="100%">
<tr>
<td align="left" nowrap="" valign="middle" width="32">
<a href="s_49.html"><img alt="previous" border="0" src="prev.png"></a>
</td>
<td align="left" valign="middle" width="30%">
<a href="s_49.html">2.1.1 Program Description</a>
</td>
<td align="center" valign="middle">
<strong>2.1.2 What is Ray-Tracing?</strong>
</td>
<td align="right" valign="middle" width="30%">
<a href="s_51.html">2.1.3 What is POV-Ray?</a>
</td>
<td align="right" nowrap="" valign="middle" width="32">
<a href="s_51.html"><img alt="next" border="0" src="next.png"></a>
</td>
</tr>
</table>
</body> </html>
|
