introduction to geometric modelling 20 september 2010

INTRODUCTION TO GEOMETRIC MODELLING

20 September 2010

Content

• Introduction• Types of 3D model• 2D vs 3D• Solid Modeling

Introduction

• 3D modeling is creating an object or a part which has 3D characteristics and can be viewed 3D

• Simply, the object has depth or thickness• In 2D drafting or drawing, the object is normally drawn in XY direction.• In 3D modeling, the object is drawn in XY

and also Z direction

3D Modeling

• Object modeled in 3D can be rotated and view from any

angle• Generally, more complicated to create and produce compare to 2D

• Types• 3 main types: wireframe, surface and solid

• 3D Wireframe Modeling– Show the ‘frame’ of the object in lines– quite similar to 2D, however the object has 3D characteristics

3D Wireframe Modeling

3D Surface Modeling

– has material/texture between the line of frame– normally no thickness– complex/advance curved surface may be produced

3D Surface Modeling

3D Solid Modeling

– model is made from solid blocks by combining and/or subtracting

– the solid blocks can be created by applying 3D operations on 2D object and/or adding and subtracting primitives

3D Solid Modeling

3D Vs 2D

2D Vs 3D

Solid Modeling

• Solid model consist of volumetric information & surface info of an object

• Surface of the model represent boundary between outside & inside of the object• Basic rule – all surfaces must touch another

surface

Solid Modeling

Solid Modeling

• Several different types of solid modeling– Primitive modeling– Constructive solid geometry (CSG)– Feature-based modeling

Primitive Modeling

• Objects described using basic geometrical forms.

• Common geometric primitives.

Primitive Modeling

Primitive Modeling

Example:

Constructive Solid Geometry

• More flexible and powerful than primitive.

• Allow Boolean Operations: union,

difference & intersection

Boolean operation

CSG: Example

CSG: Example

Feature-based Modeling

• 3D model is built using series of features, such as hole, slot, square block, etc.

• Each feature can be independent or linked to other feature.

• The geometry of each feature is controlled by modifiable constraints and dimensions.

Feature-based Modeling

FBM: 3D operations

• Basic concept– 2D cross-section or profile is produced– Depth is given to the profile• Generally 4 types– Extrude– Revolve– Sweep– Blend• *different terms might be used in different

software/books*

3D Ops: Extrude

• A linear sweep, where the profile is given a depth in straight line, perpendicular to the profile plane

• Cross-section is constant, start – end

3D Ops: Extrude

3D Ops: Revolve

• The profile is rotated around a defined axis, 0 – 360 degree• Cross-section is constant

3D Ops: Sweep

• The new command and is similar to the EXTRUDE command, but it concentrates on using paths to define the direction of the extrusion.

• This command SWEEP a 2D object along a path

3D Ops: Sweep & Blend

Steps in building 3D object

Examples of FBM + boolean