Using Scientific Visualization.


How to use this module.
This module introduces concepts of scientific visualization and shows examples of the application of visualization to data. It is intended for an audience which has access to UNIX workstations and who wish to learn how to produce their own visualization material.

Section 1 is a short introduction to general visualization concepts. Four fairly general catagories of scientific visualization are introduced: particle systems, scalar fields, vector fields and human designed objects.

Section 2 introduces DX as a programming language and shows several examples of how to use it to visualize the four catagories of data introduced in Section 1. Several DX programs are discussed in detail and may be executed and modified if you have a DX license. If you do not have a DX license, you should contact IBM for a trial DX license (see below).

Section 3 contains more extensive examples of DX programs which use the principles developed in Section 2. There are currently three topics in this section: the HPF tariff example used in another module; a graphical representation of SP2 use, and an extensive landscape generating program which uses DX to build a fractal landscape with clouds, rivers and trees.

The current version of this module uses IBM Visualization Data Explorer (DX) as the software base. In sections 2 and 3 of this module there are links which will run DX if you have installed it on the machine which is running the web browser and if you have followed these instructions so that your browser can find and execute DX.

Table of Contents:

1. Types of Scientific Visualization.

1.1 Particles
1.2 Vector and Scalar Fields
1.3 Human Designed Objects
1.4 Vis Topics not covered here
2. Visualization Techniques
2.1 Introduction to the Vis software
2.1.1 The user interface components and dataflow design.
2.1.2 The functions of specific dataflow modules.
2.1.3 The external data model.
2.1.4 The internal data model.
2.2 A simple particle system
2.3 Scalar Fields
2.4 Vector fields
2.5 Human-designed objects
2.5.1 Polyhedral Surfaces
2.5.2 Parametric Surfaces
2.5.3 Other Resources
3. Visualization Applications

3.1 Visualization of the HPF Tariff example.
3.2 SP Use Characterization.
3.3 A fractal landscape generator.

1. Types of Scientific Visualization.

Scientific visualization is a process which attempts to reformat data into forms suitable for humans. Humans have an amazingly flexible visual system which is capable of detecting complex and subtle patterns in images. To the extent that we can format data so that it conforms to the assumptions built into our visual systems (e.g. continuity, form, color), we can use human image analysis to understand data. Data may represent a broad range of phenomena which may be represented visually. In this tutorial we describe basic catagories of visualization methods, applicable across many diciplines. Topics not covered will be described briefly in Section 1.4, with some recent references.

1.1 Particles

Particle visualization includes systems represented by many similar objects, such as atoms in a tearing sheet, billiard balls colliding, or stars in a gravitational system. Visualization is necessary in such systems because of the complexity of the interactions between particles.

1.2 Vector and Scalar Fields

Field visualization includes vector fields such as flow fields or particle advection in an electric field, and scalar fields such as 3D medical scanning output or the 2D height field of a wave. Visualization is necessary in such systems because of the the complex shapes and detail on all scales such fields can have. Unlike the case of particle visualization (where the objects which move tend to be simple and known in advance), field visualization requires an extraction step in which some properties of the field are converted to geometric objects for display. Extraction steps might include isosurface generation for scalar fields or streamline production for vector fields. Details of extraction methods will be explained in 2.3 and 2.4.

1.3 Human Designed Objects

Visualization of human-designed objects includes the machines used in science and the geometry in which a computation is embedded (e.g. shape of a machine part undergoing stress analysis). In simulation, the boundary conditions of a calculation often imply a certain geometric condition or shape which needs to be shown when interpreting the results of the calculation. As an example, consider a sphere which was modeled and combined with a representation of a flow field calculated around a sphere. Sometimes calculations are carried out on CAD objects such as an automobile frame. A representation of the frame is essential to understanding the results.

1.4 Vis Topics not covered here

High Dim, Tensor fields, molecular visualization (e.g. ribbons)