Projection - TECH

Transformation of an 3D object into 2D view plane is called as projection.There are two types of projection :

1. parallel projection
2. perspective projection

Parallel projection :

The projections from the object are transformed to the view plane which is parallel to the object , then it is called as parallel projection. Its center of projection is infinite.The projection does not gives realistic view.The relative proportions between the object and its projection on the view plan is the same (i.e) L = L'. where L is the length of the object and L' is the length of the projection in the view plane.There are two types of parallel projection ,they are :

1. orthographic parallel projection
2. oblique parallel projection

Orthographic parallel projection :
The projection vector is perpendicular to the view plane. Its divided into four types :

1. top orthographic parallel projection
2. bottom orthographic parallel projection
3. side orthographic parallel projection
4. axonometric orthographic parallel projection

The top ,front and side orthographic parallel projection displays only one surfaces and the projection plane is perpendicular to the principal axis.The axonometric orthographic parallel projection displays more surfaces and the projection plane is not perpendicular to the principal axis.

Oblique parallel projection :
The projection vector is not perpendicular to the view plane.

Perspective projection :

The projection from the object are transformed to the view plane along the line that converses to a point called projection reference point (PRP) , then it is called as perspective projection.Its center of projection is finite.The projection gives realistic view.The relative proportions between the object and its projection on the view plane is not the same (i.e) L > L'.There are three types of perspective projection , they are :

1. one point perspective projection
2. two point perspective projection
3. three point perspective projection

One point perspective projection : One vanishing point and one principal axis cut by the projection plane.
Two point perspective projection : Two vanishing point and two principal axis cut by the projection plane.
Three point perspective projection : Three vanishing point and three principal axis cut by the projection plane.