Projection Matrices

Hierarchy of Projections

Perspective Projections | OpenGL

Perspective Projections

1. The visual effect of the perspective projection is similar to the human visual system known as perspective foreshortening i.e. the size of perspective projection object varies inversely with the distance of the object from COP.



2. Perspective projection does not preserve parallel lines.


3. Vanishing Point
Any set of parallel lines that are not parallel to projection plan appear to converge to a point called vanishing point.

* In this case lines parallel to x and y do not converge, only lines parallel to z do so

* One point perspective projection of a cube

* A two point perspective projection of a cube

Parallel Projections | OpenGL

Parallel Projections

In case of parallel projection instead of having COP we have direction of projection (DOP), so the perspective projection whose COP is at infinity becomes parallel projection.
In parallel projections, the lines projecting from an object onto the image plane are parallel.
Two parallel projection systems:
1. Orthographic projection

2. Oblique projection

In these the projection plane is normal and direction of projection differ.

Its major types are:
– Cabinet
– Cavalier

Projections

Projection
             Projection is the change in coordinate system and that is usually from 3D to 2D.

Projectors
             The projection of a 3D object is described by straight `projection rays' (called projectors).
Types Of Projection 

Projections can be divided into two basic
types
1. Perspective
2. Parallel
• The distinction between two is on the relation of COP and projection plane.
• If distance of one projector to another is finite then it is perspective projection otherwise it is parallel.


Perspective Projection

Parallel Projection