Collection of 2D drawings which enables you to have a complete representation of an object is called orthographic projection. Collection of 2D drawings consist of six orthographic views (Top, Bottom, Right, Left, Front and Back view) also called as six principle views.
From these six orthographic views front, right side and top view are most commonly used to represent the orthographic projection of an object. For getting the orthographic views from a 3D object there are two main types of projections used one is First angle projection and other is Third angle projection.
Main objective of both of these projections angle is to provide detail 2D drawings of 3D object but there are some differences in the way one can get the projects by using one on these methods. Following is a comparison of first angle vs third angle and a comprehensive differences between First angle and third angle projection.
Quadrant (first angle vs third angle)
To start getting projection first
divides the plane into four quadrants. For the first angle projection object is
paced in the first quadrant and for the third angle projection object is placed
is third quadrant.

Quadrants of First Angle vs Third Angle Projection 

Quadrants of First Angle Projection 

Quadrants of Third Angle Projection 
Object Placement (difference between first and third angle projection)
To get first angle projection
object is place in between the plane of projection and observer and for the
third angle projection plane of projection is placed between the object and
observer.

Object Placement of First Angle and Third Angle Projection 
State of Projection Plane (first and third angle projection)
In first angle of projection plane
of projection is taken solid while in third angle of projection it is taken as
transparent.Views Sequence (First Angle vs Third Angle)
In first angle projection right
view come in left of front view and top view come at the bottom of front view
while in third angle projection right view come on right side of front view and
top view comes at the top of front view. 
View Sequence of First Angle vs Third Angle Projection 
Symbols First Angle vs Third Angle

Symbol of First Angle vs Third Angle Projection 

First Angle vs Third Angle 
First Angle difination
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ReplyDeletethis is one of the best ways to remember, first angle projection  planes are assumed opaque, third angle projection  planes are assume transparent
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