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cube environment

English translation: 3D Mapping Technologies

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01:19 Jan 12, 2002
English to English translations [PRO]
Tech/Engineering / Computers -> Hardware
English term or phrase: cube environment
and here is the last one, :)
xxxallingus
Local time: 12:51
English translation:3D Mapping Technologies
Explanation:
"A third parameterization of environment mapping uses six cube face views directly as an environment map instead of requiring a re-warping of the cube views into a sphere map or dual-paraboloid map. To support cube mapping, the OpenGL implementation's texturing hardware is expected to directly fetch texels from the six cube face views loaded into texture memory. Existing OpenGL implementations do not support such a mode.

This approach is described by Voorhies and Foran [98]. Voorhies and Foran make two important observations. First, the expensive divider required in perspective-correct texture mapping hardware can be used by cube map texturing hardware to pre-construct the per-fragment divide necessary to project an unnormalized reflection vector to a particular cube face. Second, an efficient hardware block is proposed to compute the reflection vector per-pixel using linearly interpolated eye-space normal and eye-space position vectors. Unfortunately, efficient cube mapping requires special hardware support that is not available at the time of this writing."
See: http://www.opengl.org/developers/code/sig99/advanced99/notes...

Multiple texture support in Direct3D allows the use of environment maps for lighting and reflections. However, single-map 360-degree solutions like circular or spherical maps aren't robust enough to be widely used in real time. The most suitable solution for real-time generation and addressing of a 360-degree environment is a cubical map, composed of six textures (faces). Each face can be generated by pointing a camera with a 90-degree field-of-view in the appropriate direction. Per-vertex vectors (normal, reflection, or refraction) are provided to the rasterization hardware that then iterates them across the polygon and calculates the intersections of the interpolated vectors with the faces of the cube map. If the application or API generates the cube environment map, the driver does not require the information about the transformation matrix or coordinate space in which the per-vertex vectors are defined. This is because the vectors are used only to address the environment map, which is logically in the same coordinate space.

Addressing of a circular map involves vector normalization; addressing of a spherical map requires the use of trigonometric functions. All types of single-map environments are nonlinear: a circular map is extremely distorted and anisotropic near its periphery, while a spherical map has large distortions near its poles. This makes it necessary to re-create the environment map every time the viewpoint changes in such a way that the central view area becomes distorted.

Cubical environment maps, formed by pointing a real or simulated camera with 90-degree field-of-view in six different directions, are free of these disadvantages. They can be generated faster but need to be updated less frequently, have fewer distortions, and can be addressed by using equations similar to the ones already used for perspective-correct texture mapping.

See:
http://www.osr.com/ddk/d3d_8l2f.htm
Selected response from:

Arika
Australia
Local time: 20:51
Grading comment
This was most explanatory, thank you and hope to collaborate with you in the future :)
4 KudoZ points were awarded for this answer

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Summary of answers provided
4 +13D technology
Luciana Miquelino
3 +23D Mapping TechnologiesArika


  

Answers


29 mins   confidence: Answerer confidence 3/5Answerer confidence 3/5 peer agreement (net): +2
3D Mapping Technologies


Explanation:
"A third parameterization of environment mapping uses six cube face views directly as an environment map instead of requiring a re-warping of the cube views into a sphere map or dual-paraboloid map. To support cube mapping, the OpenGL implementation's texturing hardware is expected to directly fetch texels from the six cube face views loaded into texture memory. Existing OpenGL implementations do not support such a mode.

This approach is described by Voorhies and Foran [98]. Voorhies and Foran make two important observations. First, the expensive divider required in perspective-correct texture mapping hardware can be used by cube map texturing hardware to pre-construct the per-fragment divide necessary to project an unnormalized reflection vector to a particular cube face. Second, an efficient hardware block is proposed to compute the reflection vector per-pixel using linearly interpolated eye-space normal and eye-space position vectors. Unfortunately, efficient cube mapping requires special hardware support that is not available at the time of this writing."
See: http://www.opengl.org/developers/code/sig99/advanced99/notes...

Multiple texture support in Direct3D allows the use of environment maps for lighting and reflections. However, single-map 360-degree solutions like circular or spherical maps aren't robust enough to be widely used in real time. The most suitable solution for real-time generation and addressing of a 360-degree environment is a cubical map, composed of six textures (faces). Each face can be generated by pointing a camera with a 90-degree field-of-view in the appropriate direction. Per-vertex vectors (normal, reflection, or refraction) are provided to the rasterization hardware that then iterates them across the polygon and calculates the intersections of the interpolated vectors with the faces of the cube map. If the application or API generates the cube environment map, the driver does not require the information about the transformation matrix or coordinate space in which the per-vertex vectors are defined. This is because the vectors are used only to address the environment map, which is logically in the same coordinate space.

Addressing of a circular map involves vector normalization; addressing of a spherical map requires the use of trigonometric functions. All types of single-map environments are nonlinear: a circular map is extremely distorted and anisotropic near its periphery, while a spherical map has large distortions near its poles. This makes it necessary to re-create the environment map every time the viewpoint changes in such a way that the central view area becomes distorted.

Cubical environment maps, formed by pointing a real or simulated camera with 90-degree field-of-view in six different directions, are free of these disadvantages. They can be generated faster but need to be updated less frequently, have fewer distortions, and can be addressed by using equations similar to the ones already used for perspective-correct texture mapping.

See:
http://www.osr.com/ddk/d3d_8l2f.htm



    Reference: http://www.3dconcept.ch/artikel/environment/3.htm
Arika
Australia
Local time: 20:51
Native speaker of: Native in EnglishEnglish, Native in IndonesianIndonesian
PRO pts in pair: 4
Grading comment
This was most explanatory, thank you and hope to collaborate with you in the future :)

Peer comments on this answer (and responses from the answerer)
agree  Monica Colangelo: Quite enlightening, thank you!
1 hr

agree  Mary Maksimova
5 hrs
Login to enter a peer comment (or grade)

9 hrs   confidence: Answerer confidence 4/5Answerer confidence 4/5 peer agreement (net): +1
3D technology


Explanation:
Look at what I found:
Cube environment mapping is a technique developed by SGI a while ago and NVIDIA will be the first to bring it to home desktops. The idea is pretty simple. From an object with a reflective surface (and not from the room center, as I read somewhere else) you render six environment maps in each room direction (front, back, up, down, left, right) and use those to display the reflections on this object.

This is at the link


    Reference: http://www4.tomshardware.com/graphic/99q4/991011/geforce-04....
    Reference: http://www.opengl.org/developers/code/sig99/advanced99/notes...
Luciana Miquelino
Brazil
Local time: 07:51
Native speaker of: Native in PortuguesePortuguese

Peer comments on this answer (and responses from the answerer)
agree  Natalia Bearden: Now even I can understand it :o)
1 day 15 hrs
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