Computer Applications in Textile Engineering. Computer Applications in Textile Engineering

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Computer Applications in Textile Engineering

Sungmin Kim

http://latam.jnu.ac.kr

3. Computer Graphics

Computer Applications in Textile Engineering Computer Applications in

Textile Engineering

Introduction

• Computer Graphics

– Definition

• Research field related to the activities that includes graphics as input and output

– Importance

• Interactive shape manipulations plays a major role in CAD/CAM/CAE

• Computer graphics is an essential part of CAD/CAM/CAE

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CHONNAM NATIONAL UNIVERSITY School of Polymer Science and Engineering

Introduction

• History

CORE

SIGGRAPH (Special Interest Group on Computer Graphics) on ACM (Association for Computing Machinery)

Limited support for existing devices

GKS GKS-3D

ISO (International Standards Organization)

Standard for 2-D and 3-D graphics

PHIGS

PEX ISO Standard graphics library

for workstations

OpenGL Silicon Graphics De facto standard

2-D Graphics

• Raster Graphics

– Pixel (Picture Element) based

• Bitmap structure

• Independent processing regardless of scene complexity

• Suitable for detailed expression

• Scaling or rotation may cause quality degradation

• BMP, GIF, JPG, TIF, PCX, ...

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2-D Graphics

• Vector Graphics

– Coordinate system based

• Vector calculus

• Processing time depends on scene complexity

• Difficult to express details of an object

• Non-destructive scaling and rotation

• DXF, IGES, WMF, AI, ...

3-D Graphics

• Volume Graphics

– Voxel (volume element) based

• Space division method

• Independent processing with scene complexity

• Hardware acceleration method has not been established

• Used for medical applications

– http://www.nlm.nih.gov/research/visible/animations.html

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3-D Graphics

• Surface Graphics

– Based on geometric primitives

• Uses polygonal mesh, B-Spline, or NURBS (Non Uniform Rational B-Spline), etc.

• Processing speed depends on scene complexity

• Easy for hardware acceleration

• Used for most computer graphics applications

• Hybrid application with raster graphics

3D Graphics Basics

• Objects Representation

– Parametric surface

• Define surface by parametric function f(u,v) : R²R³

• For example, a sphere can be defined as below

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3D Graphics Basics

• Objects Representation (Cont’d)

– Polygonal mesh

• Collection of triangular elements (vertices + edges)

face normal vector

3D Graphics Basics

• Object Preparation

– Modeling packages

• 3D Studio Max

• Maya

• SoftImage

• LightWave

– 3D scan data

• RapidForm

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3D Graphics Basics

• Lighting

– Importance

• Lighting enhances the reality of scene

• Realistic appearance may be a crucial factor for specific application

– Difficulties

• Effects of various light sources and colors – Sun, fire, light bulb, ...

• Effects of material surface property and color – Shiny, dull, ...

3D Graphics Basics

• Lighting (Cont’d)

– Light sources

Directional (Parallel)

Spot (Specular) Point

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3D Graphics Basics

• Lighting (Cont’d)

– Ambient lighting

• Effect of indirect lighting

• Realization of color

– Diffuse lighting

• Shading effect

– Specular lighting

• Creating highlights

3D Graphics Basics

• Shading

– Evaluation of lighting equation

• Calculate for each vertex on the mesh

• Interpolate for the rest of the mesh

– Type

• Flat shading

• Gouraud shading

• Phong shading

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3D Graphics Basics

• Shading (Cont’d)

– Gouraud shading

• Evaluate color at each vertex

• Interpolate the color of interior points

Interpolate Color

3D Graphics Basics

• Shading (Cont’d)

– Phong shading

• Interpolate normal vectors for interior points

• Evaluate lighting equation for each point

• More accurate shading

• Realization of specular light (highlight)

Interpolate

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3D Graphics Basics

• Texture Mapping

– Importance

• Enhance visual quality of object without increasing scene complexity

– Procedure

• Prepare 2D texture image

• Assign texture coordinates to each vertex

3D Graphics Basics

• Rendering

– Global lighting (Illumination)

• Color is determined by multiple interactions among light sources and reflective surfaces

• Recursive reflection of light between surfaces accounts for subtle shading

– Type

• Ray casting

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3D Graphics Basics

• Rendering (Cont’d)

– Ray tracing

• Rendering technique that mimics physical processes of light

• Extremely intensive computation – Transparency

– Refraction and reflection – Lighting and shadow

Computer Applications in Textile Engineering. Computer Applications in Textile Engineering