POV-Ray

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POV-Ray
Developed by	The POV-Team
Latest release	3.6 / July 12, 2004
Preview release	3.7.beta.25b / February 8, 2007
OS	Cross-platform
Genre	Ray tracer
License	POV-Ray License
Website	www.povray.org

The Persistence of Vision Raytracer, or POV-Ray, is a ray tracing program available for a variety of computer platforms. It was originally based on DKBTrace, written by David Kirk Buck and Aaron A. Collins. There are also influences from the earlier Polyray raytracer contributed by its author Alexander Enzmann. POV-Ray is freeware with the source code available.

[edit] History

Some time in the 1980s, David Kirk Buck downloaded the source code for a Unix raytracer to his Amiga. Interested, he played with it for a while, eventually deciding to write his own raytracer, named DKBTrace after his initials. He posted it to his bulletin board system, thinking others might be interested in it. In 1987, Aaron A. Collins downloaded DKBTrace and began working on an x86-based port of it. He and David Buck collaborated to add several more features. When the program proved to be more popular than anticipated, they could not keep up with demand for more features. Thus, in July 1991 David turned over the project to a team of programmers. At the same time, he felt that it was inappropriate to use his initials on a program he no longer maintained. The name "STAR" (Software Taskforce on Animation and Rendering) was considered, but eventually the name became the "Persistence of Vision Raytracer", or "POV-Ray" for short.^[1]

POV-Ray was the first ray tracer to render an image in orbit, rendered by Mark Shuttleworth inside the International Space Station.^[2]

Features of the application and a summary of its history are discussed in an interview with David Kirk Buck and Chris Cason on episode 24 of FLOSS Weekly ^[3].

[edit] Features

Glass scene rendered in POV-Ray, demonstrating radiosity, photons, focal blur, and other photorealistic capabilities

POV-Ray has matured substantially since it was created. Recent versions of the software include the following features:

• A Turing-complete scene description language (SDL) that supports macros and loops.^[4]
• Library of ready-made scenes, textures, and objects
• Support for a number of geometric primitives and constructive solid geometry
• Several kinds of light sources
• Atmospheric effects such as fog and media (smoke, clouds)
• Reflections, refractions, and light caustics using photon mapping
• Surface patterns such as wrinkles, bumps, and ripples, for use in procedural textures and bump mapping
• Radiosity
• Image format support for textures and rendered output, including TGA, PNG, JPEG (only input) among others
• Extensive user documentation

One of POV-Ray's main attractions is its large collection of third party support. A large number of tools, textures, models, scenes, and tutorials can be found on the web. It is also a useful reference for those wanting to learn how ray tracing and related geometry and graphics algorithms work.

[edit] Current version

The current official version of POV-Ray is 3.6. Some of the main features of this release:

• Extends UV-mapping to more primitives.
• Adds 16 and 32 bit integer data to density file.
• Various bugfixes and speed-ups.
• Improved 64 bit compatibility.

Beta-testing of version 3.7 is underway as of fall 2006. The main improvement over 3.6 will be SMP support to allow the renderer to take advantage of multiple processors. Additionally, support has been added for HDRI, including the OpenEXR and Radiance file formats, and improved bounding using BSP trees.

In July 2006, Intel corporation started using the beta version to demonstrate their new dual-core Conroe processor due to the efficiency of the 3.7 beta's SMP implementation.^[5]

[edit] Primitives

Some dice rendered in POV-Ray. Constructive solid geometry, refraction and focal blur are demonstrated.

POV-Ray, in addition to standard geometric shapes like tori, spheres and heightfields, supports mathematically defined primitives such as the isosurface (a finite approximation of an arbitrary function), the polynomial primitive (an infinite object defined by a 15th order or lower polynomial), the julia fractal (a 3-dimensional slice of a 4-dimensional fractal), the superquadratic ellipsoid (intermediate between a sphere and a cube), and the parametric primitive (using equations that represent its surface, rather than its interior).

POV-Ray internally represents objects using their mathematical definitions; all POV-Ray primitive objects can be described by mathematical functions. This is different from many 3D computer modeling packages, which typically use triangle meshes to compose all objects.

This fact provides POV-Ray with several advantages over other rendering / modeling systems. POV-Ray primitives are more accurate than their polygonal counterparts. Objects that can be described in terms of spheres, planar surfaces, cylinders, tori and the like are perfectly smooth and mathematically accurate in POV-Ray renderings, whereas polygonal artifacts may be visible in mesh-based modeling software. POV-Ray primitives are also simpler to define than most of their polygonal counterparts. In POV-Ray, a sphere is described simply by its center and radius; in a mesh-based environment, a sphere must be described by a multitude of small polygons.

On the other hand, primitive-, script-based modeling is not always a practical method to create objects such as realistic characters or complex man-made artifacts like cars. Those objects have to be created in mesh-based modeling applications such as Wings 3D or Blender and then converted to POV-Ray's own mesh format.

[edit] Examples of the Scene Description Language

The following is an example of the scene description language used by POV-Ray to describe a scene to render. It demonstrates use of the camera, lights, a simple box shape and the transforming effects of scaling, rotation and translation.

POV-Ray image output based on the script to the left

#version 3.6;
 #include "colors.inc"
 global_settings { assumed_gamma 1.0 }
 
 background   { color rgb <0.25, 0.25, 0.25> }
 
 camera       { location  <0.0, 0.5, -4.0>
                direction 1.5*z
                right     x*image_width/image_height
                look_at   <0.0, 0.0, 0.0> }
 
 light_source { <0, 0, 0>
                color rgb <1, 1, 1>
                translate <-5, 5, -5> }
 
 light_source { <0, 0, 0>        
                color rgb <0.25, 0.25, 0.25>
                translate <6, -6, -6> }
 
 box          { <-0.5, -0.5, -0.5>
                <0.5, 0.5, 0.5>
                texture { pigment { color Red }
                          finish  { specular 0.6 }
                          normal  { agate 0.25 scale 1/2 } }       
                rotate <45,46,47> }

The following script fragment shows the use of variable declaration, assignment, comparison and the while loop construct:

POV-Ray image output based on the script to the left

#declare the_angle = 0;
 
 #while (the_angle <= 360)
        box {   <-0.5, -0.5, -0.5>
                <0.5, 0.5, 0.5>
                texture { pigment { color Red }
                          finish  { specular 0.6 }
                          normal  { agate 0.25 scale 1/2 } }
                rotate the_angle }
        #declare the_angle = the_angle + 45;
 #end

[edit] Development and maintenance

Official modifications to the POV-Ray source tree are done and/or approved by the POV-Team. Most patch submission and/or bug reporting is done in the POV-Ray newsgroups on the povray.org news server. Since POV-Ray's source is available there are unofficial forks and patched versions of POV-Ray available from third parties; however, these are not officially supported by the POV-Team.

Official POV-Ray versions currently do not support shader plug-ins^[6]. Some features, like radiosity and splines are still in development and may be subject to syntactical change.

[edit] Platform Support

POV-Ray is distributed in compiled format for Macintosh, Windows and Linux. Support for Intel Macs is not available in the Macintosh version, but since Mac OS is a version of Unix the Linux version can be compiled on it. POV-Ray also could be ported to any platform which has compatible C++ compiler.

People with Intel Macs can use MegaPOV though, as that is compiled as Universal Binary.

[edit] Licensing

POV-Ray is distributed under the POV-Ray License, which permits free distribution of the program source code and binaries, but restricts commercial distribution and the creation of derivative works other than fully functional versions of POV-Ray.

Although the source code is available for modification, due to specific restrictions, it is not open source according to the OSI definition of the term. One of the reasons that POV-Ray is not licensed under the free software GNU General Public License (GPL), or other open source licenses, is that POV-Ray was developed before the GPL-style licenses became widely used; the developers wrote their own license for the release of POV-Ray, and contributors to the software have worked under the assumption that their contributions would be licensed under the POV-Ray License.

The whereabouts of some of the contributors to the source code are unknown, and therefore the license cannot be changed, since the permission of all contributors would be required.

A complete rewrite of POV-Ray ("POV-Ray 4.0") is currently under discussion, which would use a more liberal license, most likely GPL v3^[7].

[edit] See also

• YafRay (Yet Another Free Raytracer)
• Kerkythea Free ray tracing program with enhanced Sketchup compatibility
• Sunflow an open source rendering system for photo-realistic image synthesis written in Java
• Blender (software) a free and open-source software program for 3D modeling, animation, and rendering

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