ch12 view1

7/29/2019 ch12 view1

1/29

p_16

_10

@hotmail.comit4ever2008 @hotmail.com 1

University of PalestineComputer Graphics

ITGD3107

Prepare:Mohammed J. el-masre

Nidal M. El-Borbar

Supervision:Dr. Sana'a

Presentation name :Three Dimensional Viewing

7/29/2019 ch12 view1

2/29

p_16

_10


Contents

3D ViewingCamera AnalogyViewing Pipeline

Camera Modeling w/ OpenGLProjectionsTypes of ProjectionsPerspective ProjectionParallel ProjectionProjection Matrix

Projection of Lines3D Viewing with OpenGLMatrix ModesThree Dimensional Viewing

7/29/2019 ch12 view1

3/29

p_16

_10


3D ViewingThe steps for computer generation of a view of a three

dimensional scene are somewhat analogous to the

processes involved in taking a photograph.

7/29/2019 ch12 view1

4/29

p_16

_10


Camera Analogy

Position

Orientation

Window (aperture)

of the camera

1. Viewing position

2. Camera orientation

3. Size of clippingwindow

7/29/2019 ch12 view1

5/29

p_16

_10


Viewing PipelineThe general processing steps for modeling and

converting a world coordinate description of a

scene to device coordinates:

7/29/2019 ch12 view1

6/29

p_16

_10


7/29/2019 ch12 view1

7/29

p_16

_10


Viewing Pipeline1. Construct the shape of individual objects in a scene within modeling

coordinate, and place the objects into appropriate positions within the scene

(world coordinate).

7/29/2019 ch12 view1

8/29

p_16

_10


Viewing PipelineWorld coordinate positions are converted to viewing

coordinates.

7/29/2019 ch12 view1

9/29

p_16

_10


Viewing PipelineConvert the viewing coordinate description of the

scene to coordinate positions on the projection

plane.

7/29/2019 ch12 view1

10/29

p_16

_10


Viewing Pipeline

Positions on the projection plane, will then mapped

to the Normalized coordinate and output device.

7/29/2019 ch12 view1

11/29

11

Camera Modeling w/ OpenGLcamera coordinatesystem

viewport coordinate

system

device/screen

coordinate system

7/29/2019 ch12 view1

12/29

Coordinate Systems

World Coordinate System-This is object space or the space in

which the application model is defined.

Screen Coordinate System-The space in which the image is

displayed.World Window (or clipping)-This is the rectangle in the world

defining the region that is to be displayed.

Viewport-The rectangular portion of the interface window that

defines where the image will actually appear (usually theentire interface window but in some cases modified to be a

portion of the interface window).

Viewing Transformation-The process of mapping a world

window in World Coordinates to the Viewport.12

7/29/2019 ch12 view1

13/29

Window to Viewport mapping

Window-to-Viewport mapping is the process of

mapping or transforming a two-dimensional,world-coordinate scene to device coordinates. In

particular, objects inside the world or clipping

window are mapped to the viewport. The viewport

is displayed in the interface window on the screen.In other words, the clipping window is used to

select the part of the scene that is to be displayed.

The viewport then positions the scene on the

output device. 13

7/29/2019 ch12 view1

14/29

Projection plane

1. Projection plane called the view plane in

computer graphics

2. It is defined by a point called view

reference point (VRP) and a normal (a

vector perpendicular to the plane) called

view plane normal (VPN).

14

7/29/2019 ch12 view1

15/29

Viewing Coordinates

View Reference point: It is the center of viewing

coordinate system. It is chosen to be close to or onsurface of object in a scene.

View Plane normal vector: This normal vector is in

a direction perpendicular to view plane.

View Distance: It is the distance from view plane to

view reference point. 15

7/29/2019 ch12 view1

16/29

Positioned by a View distance

16

7/29/2019 ch12 view1

17/29

17

Projections

Once the view volume isdetermined, aprojectiontransformation willconvert the object inthe 3D view volume toa 2D image on the

projection plane.

7/29/2019 ch12 view1

18/29

18

Types of Projections

Perspective ProjectionParallel Projection

7/29/2019 ch12 view1

19/29

19

Perspective Projection (1/2)

Give a realistic view of 3D objects, but doesnot preserve shape of object or scale

Perspective images of parallel lines notparallel with projection plane converge to apoint called vanishing point or projectionreference point.

Size of object is diminished with distance Used in architectural, engineering, industrial

design, and advertising drawings

7/29/2019 ch12 view1

20/29

20

Perspective Projection (2/2)

3-point perspective

1-point perspective

2-point perspective

Most popular

7/29/2019 ch12 view1

21/29

21

Parallel Projection

Accurate and same-scale measurements

Not realistic, and may require multipleprojections to get a complete feeling of theobject

Used in drawings of machine parts and inworking architectural drawings

7/29/2019 ch12 view1

22/29

Orthographic ProjectionProjectors are orthogonal to projection surface

22

7/29/2019 ch12 view1

23/29

Multiview Orthographic Projection

1. Projection plane parallel to principal face2. Usually form front, top, side views

p_16_10 @hotmail.comit4ever2008 @hotmail.com 23

7/29/2019 ch12 view1

24/29

Axonometric Projections

Allow projection plane to move relative

to object

24

7/29/2019 ch12 view1

25/29

Types of

Axonometric Projections

25

7/29/2019 ch12 view1

26/29

Oblique Projections

Projectors not orthogonal to projection plane

The projection plane is typically parallel to a face of the

object

Classified by the angle between projector and plane

Pi/4: Cavalier type

Preserves the lengths of edges orthogonal to projection

plane. Cavalier: 45 degree ArcTan(2): Cabinet type

Halves the lengths of edges orthogonal to projection plane

Cabinet: arctan(2) =63.4 degree

26

7/29/2019 ch12 view1

27/29

Types of Perspective Projections

Based on number of vanishing points for

lines parallel to the three coordinateaxes

Determined by number of axes parallel

to the viewing plane

27

7/29/2019 ch12 view1

28/29

Types

28

7/29/2019 ch12 view1

29/29

p_16_10 @hotmail.comit4ever2008 @hotmail.com 29

ch12 view1

Documents