Topic 43d Modelling

Concepts

Objectives• Students should be able to:

– Understand the concept of Space, Object and structure

– Build objects with numbers– Transform object – Understand file format for modelling– Practice modelling strategy

Space, Objects & Structures• Modelling - Spatial description and

placement of imaginary 3 dimensional objects, environments and scenes with computer system.

Space, Objects & Structures• We live in 3 Dimensional

world.• So, Modelling 3

Dimensional object is based on building real object and should consider:– Measuring spaces– Building objects– Arranging them in

structures

• Measuring spaces – The measurements are taken from the

real object/model.– In 3D environment, the Modelling space

is called workspace/scene.– The measurement is based on the

rectangular coordinate system.

Space, Objects & Structures

Space, Objects & Structures

• Building objects – To build objects, using computer

software that describe a shape in numbers.

– The data is stored in geometry files.– The object is built from the basic

elements (points, lines and surfaces).

Space, Objects & Structures

• Arranging them in structures – The object is moved around in space

or scene.– The arrangement is called geometric

transformation.– The transformation is based on the

XYZ co-ordinate system.

Rectangular/Cartesian Coordinate System

Space, Objects & Structures• 3D space with the boundaries -

workspace/scene.• The main point of reference - origin.• Have 3 basic dimensions:

– Width – represented by X-axis– Height – represented by Y-axis – Depth – represented by Z-axis

• Rectangular/Cartesian Coordinate System is used to define specific locations and position of objects in 3D space.

Building with Numbers• 3D Computer Modelling

requires very precise description of shape.

• The example is using numbers to specify the:– Position– Radius– Height– Number of sides

Building with Numbers• Most 3D software will create

a data file to define models in a way that can be understood by the computer system.

• The files that contain the data describing the object are called geometry files.

Points, Lines and Surface• Points, lines and surface are among

the basic elements to build 3D objects.

• Point - defined by its XYZ location• Line - defined by the XYZ location of

its two endpoints• Edge - defined by two adjoining

surfaces• Surface - defined by the position of

its bounding lines

• Geometric Transformation - the functions used for modifying shape, size/ proportion and position of objects in space.

• Geometric transformations can be performed on single objects or on entire environments.

Transformation of Object

Transformation of Object

• Transformation that are applied to the objects using the environment’s axes/origin are called global transformation.

• Transformation that are applied to a single object or a limited selection of objects, using the object’s own axes and origin are called local transformation.

Transformation of Object• The object’s center and axis usually used

as the centres of rotation and scaling, and the axis of translation, rotation and scaling.(unless specified)

• Performing global transformations, or local transformations that occur along or around the global axis, the order in which transformations are applied to an object or a series of objects can affect the final result.

Transformation of Object• Rotation and scaling sequences should be

planned carefully. (Although translation sequences can be applied in any order).

• A series of global transformation applied in a sequences sometimes called Concatenated transformation.

Absolute or Relative Values• Common techniques to apply

transformation to one or several objects is by selecting them and dragging them to a new location in 3D space.

• Its common to use the mouse and the mouse button to control position, orientation, and size of the models in the environment.

Absolute or Relatives Values• But it is necessary to type specific values

on the keyboard for controlling the exact position, orientation, and size of model.

• When typing a values become necessity, all the transformations can be specified as absolute values or as relative values.

Absolute or Relative ValuesAbsolute Values

• Always refer to an exact position in space where the object must be relocated regardless of where the object was located in space before the transformation.

Relatives Values• Are numerical values that express the number

of units that must be added or subtracted to the current position of the object.

• Relative to an existing absolute positions.

Absolute or Relatives ValuesExample:

• A sphere located at XYZ coordinate, (30 30 30)

(30 50 30) (0 20 0)

trans sphere 0 20 0 (absolute)trans sphere 0 20 0 (relative)

• Move an object or group of objects in a linear way to a new location in 3D space.

• Can occur along one axis or along several axes at the same time.

Translation

• Move an object or group of objects around specific center and axis.

• The amount of rotation specified in terms of an angle of rotation (measured in degrees) and a direction of rotation.

• Object can be rotated around their own centre, the centre of the environment, or even the centre of the ‘parent’ in a hierarchy of object.

Rotation

• Geometric transformation used to change the size and/or the proportion of an element or a group of elements.

• Can be applied to an object in a proportional or a non- proportional mode.

Scaling

ScalingProportional Scaling• Consist of resizing an object along

each axis in equal amounts.• The result – always a larger or smaller

object with the same proportions as the original object.

Non proportional scaling• Resized by different factors along each

axis.• Change the proportion of 3Dobject to

becomes taller or shorter, wider or narrower, or deeper or shallower.

• Usually used to simulate the ‘squash and stretch’ distortions typical of 3D object in motion.

Scaling

• A type of drawing or rendering, that graphically approximates on a planar (two-dimensional) surface the images of 3D objects so as to approximate actual visual perception.

• Is a transformation that happens automatically in virtually all 3D software.

Perspective Projection

• Refers to the motions that place the camera in different parts of the scene.

• Can be used during Modelling process.• The spherical or azimuthal coordinate

system is often used to navigate through the world by specifying camera positions in terms of the camera’s angle around the horizon, its angle above the horizon, and its distance from the object.

Navigation

Point of Interest

Pan

Orbit

Spherical Or Azimuthal Coordinate SystemNavigation

• The characteristic of a camera in 3D space are defined by:– camera position, – its point of interest, – camera lens.

Navigation

NavigationType of movement:• Dolly – translation of the

camera along its X axis• Boom – translation along its Y

axis• Tuck - translation along Z axis• Tilt (pitch)– rotation of the

camera around X axis• Roll - rotation along its Z axis• Pan (yaw) – rotation along its

Y axis• Zoom – special camera move

File Formats for Modelling• Many of file formats containing

descriptions of object geometry are exclusively to specific computer program and are not portable (proprietary).

• All 3D models are created that can be saved and retrieved in application’s own native file format.

• Files saved in native formats usually load faster and require less space for storage.

• Conversion utilities can translate geometry files in native format between applications.

File Formats for Modelling• Universal file format is used for transporting geometry

information between modelling program:• Some popular 3D file formats:

3D Studio Mesh 3ds

3DS MAX max

Autodesk AutoCAD dxf

Autodesk AutoCAD dwg

DirectX model x

LightWave 3D Object lwo

LightWave Scene lws

Softimage xsi

SolidWorks sldasm, sldprt

Universal 3D u3d

Unreal Character File psk

Virtual Reality Modeling Language (VRML) Worlds wrl, vrml

Wavefront Object obj

Basic Modelling Strategies• Sketch your ideas

– On paper or using clay – quick study, rough drawing, a draft.

• Use multiple camera views while Modelling– Get image from different angles / views.– Front, side, top and camera view.

• Write your numbers down– General dimensions, positions, boundaries.

• Do not lose the blueprints– May need to re-model or modify the objects.

Basic Modelling Strategies• Is the model to be used for CAD/CAM?

– Object are modeled to be rendered and animated are built differently from objects to be served for CAD/CAM.

• Modelling is related to rendering and animation– It is important to check the polygon count of

the model.• Check the preferences file formats.• Check your memory requirements.• Save your work often.