Types of Projection in Computer Graphics

 

Projection in Computer Graphics:

Projection is a technique which is used to transform a 3D object into a 2D plane. It is defined as the mapping or transformation of the object in a view plane. The view plane is displayed surface.

Types of Projection:

In Computer Graphics, there are mainly two types of projection, these are:
1. Parallel Projection
2. Perspective Projection

Parallel Projection:

When the centre of projection situates at an infinite distance such that the projectors are parallel to each other. These type of projection says Parallel Projection.

In Parallel Projection, the image points are found at the intersection of the view plane with parallel projectors drawn from the object points in a fixed direction. The two basic types of parallel projection are:
i. Oblique Projection
ii. Orthographic Projection

 

        i.            Oblique projection

·         When the angle between the projectors and the plane of projection isn’t equal to 90 then the projection says oblique projection.

·         In oblique projection, the direction of projection is not normal to the projection of plane.

·         We can view the object better than orthographic projection.

·         There are 2 types of oblique projection:

o   Cavalier

o   Cabinet

 

 

 

Cavalier Projection:

The projection line making an angle 45 degree with projected plane, as a result the line of the object length will not change.

 

Cabinet Projection:

It makes 63.4-degree angle with the projection plane. Here lines perpendicular to the viewing surface are projected at ½ their actual length.

 

 

      ii.            Orthographic projection

·         In orthographic projection the direction of projection is normal to the projection of the plane.

·         In orthographic lines are parallel to each other making an angle 90 degree with view plane.

 

·         There are 3 types of orthographic projections-

o   Front projection

o   Top projection

o   Side projection

 

 

Perspective Projection:

·         The projection is said to be perspective projection, if the center of projection is at finite distance from the projected plane.

·         Visual effect is similar to human visual system.

·         Objects appear smaller as distance from center of projection (eye of observer) increases.

·         Difficult to determine the exact size and shape of object.

 

 

·         There are 3 types of perspective projections:

o   One point perspective projection

o   Two point perspective projection

o   Three point perspective projection

 

 

 

 

 

It is the point where all lines will appear to meet. There can be one point, two point, and three-point perspectives.

 

 

 

 

o   One point: There is only one vanishing point as shown in fig (a)

o   Two points: There are two vanishing points. One is the x-direction and other in the y-direction as shown in fig(b)

o   Three points: There are three vanishing points. One is x second in y and third in two directions.

 

In perspective projection lines of projection do not remain parallel. The lines converge at a single point called a center of projection. The projected image on the screen is obtained by points of intersection of converging lines with the plane of the screen. The image on the screen is seen as of viewer’s eye were located at the Centre of projection, lines of projection would correspond to path travel by light beam originating from object.