Parallel Projections:

Parallel projections catagorize one of two chief subclasses of planar geometric projections. Projections in this subclass contain two common characteristics. The primary characteristic concerns the placement of the centre of projection (PRP) that represents the camera or viewing location. In a parallel projection, the camera is situated at an infinite distance from the view plane .By placing the camera at an infinite distance from the view plane, projectors to the view plane become parallel (the second characteristic of a parallel projection).

Figure shows the projection of line AB to the view plane. In this case, the measurement of line AB is maintained in the projected line A'B'. Whereas the measurements of an object are not preserved in all of the parallel projections, the parallel nature of projectors maintains the proportion of an object along a major axis. Thus, parallel projections are useful in applications needing the relative proportions of an object to be maintained.

Figure: Parallel Projection Defined by the Centre of Projection (PRP) Placed at an Infinite Distance from the View plane