Orthographic Projection is a way of representing 3D objects in 2D. In orthographic projection the front, top and side views are shown separately.
If straight lines are drawn from the various points on the contour of an object to meet a plane, the object is said to be projected on the plane. The figure formed by joining in correct sequence, the points at which these lines meet the plane is called a projection of the object.
The straight lines which are passed through an object and projected on the plane are called projection. or A projection is defined as a view imagined to be projected on to a plane known as the projection plane.
While projecting, if the “rays of sight” (projectors) are taken perpendicular to the plane of projection. The projection method is then called orthographic projection. In this method the observer is assumed to be at definite distance from the plane of projection, such that the projectors will be parallel to each other.
Orthographic views consists of one, two or more separate views of an object taken from different directions, generally at right angles to each other and arranged in a different manner. These views collectively describe the object. Orthographic views of any object can be represented by any one the two systems of projections.
The First angle projection and Third angle projection. These are named according to the quadrant in which the object is imagined to be placed for purposes of projection. As far as the shape and size of the views are concerned there is no difference between these two.
Mechanical Basics First Angle & Third Angle Projection