Principal Planes of Orthographic Projection
Orthographic projection uses two main planes called the principal planes of projection, they are the vertical plane planes and the horizontal planes.
These two planes intersect, producing four quadrants. The object to be drawn is imagined to be placed in one of these quadrants, and orthographic views of it are projected onto the planes.
The object is normally positioned so that its main faces are parallel to them. This ensures that views of the faces are true sizes and shapes.
Principal Planes of Projection:
1. Vertical Plane: The views on the vertical plane are front elevation and end elevation (side elevation).
2. Horizontal plane: The plan is shown on the horizontal plane.
The figure above shows the intersection of the vertical and horizontal planes at right angles. This intersection forms four angles, the first angle, second angle, third angle, and fourth angle.
The quadrant 0 – 90° contains the first angle and the quadrant 180°- 270° contains the third angle.
In orthographic projection, only the first and third angles are used.
Since the second and fourth quadrants would combine the two systems, we do not use them.