3D Visualisation of Simulation Data.

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3D Visualisation of Simulation Data.
Informal Seminar 08/03/2004. By Chris Sweet.
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Why Visualise?

• More meaningful than lists of numbers.
• People have good visual intuition of dynamics.
• Visual check that simulation is correct.
• Easier to communicate interesting features of the
  simulation to others.

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Methods for 3D Output.

• Projection of 3D image onto 2D plane.
• 3D libraries such as OpenGL or DirectX.

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Projection of 3D onto 2D

• This can be accomplished by using a matrix to
  project the 3D data onto a 2D plane, which can be
  varied to change the viewpoint.
• For a viewing plane defined as follows we get a
  transformation matrix

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Projection of 3D onto 2D

• Example of 2D rendering of objects in 3D.

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Projection of 3D onto 2D

• Example of 3D surface rendering.

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Advantages/Disadvantages of 3D Projection

• Easy to implement on any platform with raster
  graphics.
• -Objects drawn as 2D.
• -Hard to determine depth from viewer, (front
  objects do not obscure rear objects).
• -Hard to implement perspective.
• -Hard to apply textures.
• -Slow as pixel driven.

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Advantages/Disadvantages of 3D Libraries

• -Hard initial implementation.
• All methods of depth/ perspective/ texturing
  looked after.
• Hardware support for drawing so fast.
• Libraries exist for many different platforms.

• Comparison 3D projection of Solar System.

• 3D library rendering of Solar System.

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Advantages/Disadvantages of 3D Libraries

• Comparison 3D projection of Solar System.

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Advantages/Disadvantages of 3D Libraries

• 3D library rendering of Solar System.

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OpenGL

• OpenGL is a cross-platform 3D graphics and
  modelling library with extremely good hardware
  support.
• OpenGL is a procedural graphics API containing
  over 200 commands and functions.
• OpenGL works in conjunction with other libraries,
  such as GLUT, for easier implementation.

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OpenGL basics, Vertex Transformation

• Vertices are transformed according to the
  following pipeline

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OpenGL basics, Initialisation.

• Typical C initialisation commands
• Typical C re-draw commands

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OpenGL View/Perspective

• The viewing Frustum parameters are set using the
  command
• According to the diagram

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OpenGL Drawing Objects

• All OpenGL objects are constructed from polygons
  by defining the vertices
• or by using GLUT more complex shapes

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OpenGL Lighting

• Both ambient and point source lighting can be
  defined

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OpenGL Textures

• Textures can be mapped onto objects according to
  their vertex positions

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OpenGL Translate/Rotate Object

• OpenGL objects can and rotatedbe
  translated

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OpenGL Solar System Model

• The Solar System model is a 10 body model
  designed to test the long term stability of
  different integrators and uses the previous
  OpenGL techniques to generate the graphics.

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References/Acknowledgments

• The following book provides a good reference to
  OpenGL with examples in C/C OpenGL SuperBible
  by R.S.Wright, M.Sweet (No relation!).
• The following online tutorial covers most aspects
  of OpenGL programming http//nehe.gamedev.net/