First Angle Projection and Third Angle Projection

This is one of the most commonly discussed topics in the community of both mechanical engineers and designers. Students who are new to the concept of orthographic drawings often get confused between the two, and if you’re one of them, you’re not alone, but soon you will overcome this once you have read this article. Ask any professional with good experience in design and tools; they will say that this is nothing but only the means of representing three-dimensional objects in two dimensions. 

The first and third angle projections are nothing but ways of describing an object’s looks from different directions. This is called orthographic projection. The orthographic is simply the engineering drawings or plan views. Now that you are aware of the concept of orthographic projections and understand it well let’s discuss the difference between first and third angle projection in detail.

First Angle Projection: 

In the first angle projection, the object is put in the 1st quadrant of the two-dimensional plane. The object is placed at the top of the horizontal plane and the front of the vertical plane. The first angle projection is widely used in our country and most of the European countries. The object is always put between the observer and projection planes. The plane of projection is always taken as solid in the first angle projection.

It is represented as

Third Angle Projection: 

In the third angle projection, the object is put in the third quadrant. The object is placed at the bottom of the horizontal plane and behind the vertical planes. Third angle projection majorly opts in the United States. In this projection, the projection planes come between the object and the observer. The plane of projection is always taken as transparent in the third angle projection.

It is represented as

The Difference Between First and Third Angle Projection

Fundamentals of first and third angle projection

The first angle projection is one of the ways to represent three-dimensional objects in two dimensions which is widely used in Europe and most of the world but the United States. For obtaining the orthographic views from 3D objects, we divide the plane into four quadrants. For the projection in the first angle projection, the object is placed in the first quadrant. The United States and Australia use the Third Angle Projection method because of their default projection system. Here in the third angle projection, the object is placed in the third quadrant.

How are the first and third angle projections represented?

Both of these projection methods are used for multi-view projection of three-dimensional objects using different two-dimensional drawings. The principal planes of an object are used to represent different views of the same object from various points of view. To obtain the projection in the first angle projection, the object is placed in the first quadrant, which means it’s placed between the plane of projection and the observer. For the projection of the object in the third angle projection, the object is placed below and behind the plane of view, meaning the plane of projection is between the observer and the object.

The first and third angle projection plane

Both of the methods of orthographic projection result in the same six principal views of the object but the arrangement of views and the state of the plane of projection. In the first angle projection, the plane of projection is taken as opaque or solid or non-transparent. The object is put in front of the planes, and each view is pushed through the object places the vertical plane behind the object and pushes the horizontal plane Below it. While in the third angle projection, the plane of projection is taken as transparent, and the object is placed behind the vertical plane and below the horizontal plane.

First and third angle projection viewing sequence

While we talk about the first angle projection scheme, the orthographic view is projected on a plane located behind the object, and the observer is on the left concerning the object and projects the side view on a plane behind the object. The right side view concerning the object is projected to the left of the front view, and the top view is projected onto the bottom of the front view, below the object. Whereas in the third angle projection scheme, the observer is on the right concerning the object and the orthographic view is projected on the plane that is located between the viewpoint and the object. The right view is projected onto the right side of the front view, and the top view is projected above the front view, above the object.

Summary of the difference