7 Difference Between First Angle And Third Angle Projection

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First Angle and Third Angle are two methods orthographic projection used in technical drawing and normally comprises the three views (perspectives): front, top and side. In other words, Orthographic projection is a way of drawing a 3D object from different directions.

 Usually front, top and side views are drawn so that a person looking at the drawing can see all the important sides. Orthographic drawings are useful especially when a design has been developed to a stage whereby it is almost ready to manufacture. First angle and third angle only differ in the position of the top, front and side views.

First Angle Projection

First angle projection is a method of creating a 2D drawing of a 3D object. In first angle, the object is placed in the first quadrant. This means that the vertical plane is behind the object and the horizontal plane is underneath the object. First angle projection method is used in Europe, India, Canada and the rest of world as a default projection system.

What You Need To Know About First Angle Projection

  • The object is placed in the first quadrant for the first angle projection.
  • To get the first angle projection, the object is placed between the plane of projection and the observer.
  • In the first angle projection schema, the plane of projection is assumed to be opaque or non-transparent. The object is placed in front of the planes and each view is pushed through the object which places the vertical plane behind the object and pushes the horizontal plane underneath.
  • In the first angle projection, the orthographic view is projected on a plane located beyond the object and the observer is on the left side of the object and projects the side view on a plane beyond the object.
  • The right side view is projected to the left of the front view and the top view is projected onto the bottom of the front view.
  • First angle projection method is used in Europe, India, Canada and the rest of world as a default projection system.

First Angle Projection Symbol

Third Angle Projection

Third angle projection is a method of creating a 2D drawing of a 3D object. In third angle, the object is placed in the third quadrant. This means that the plane of projection is between the observer and the object. Third angle projection is used in Australia and United States as a default projection system for industrial designs for product fabrication.

What You Need To Know About Third Angle Projection

  • The object is placed in the third quadrant for the third angle projection.
  • To get a third angle projection, the plane of projection is between the observer and the object.
  • In the third angle projection, the plane of projection is assumed to be transparent and the object is placed below the horizontal plane and behind the vertical plane.
  • In third angle projection, the observer is on the right side of the object and the orthographic view is projected on a plane located between the view point 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.
  • Third angle projection is used in Australia and United States as a default projection system for industrial designs for product fabrication.

Third Angle Projection Symbol

Also Read: Difference Between Parallel And Perspective Projection

First Angle Vs Third Angle Projection In Tabular Form

BASIS OF COMPARISON   FIRST ANGLE PROJECTION THIRD ANGLE PROJECTION
Object Placement The object is placed in the first quadrant for the first angle projection.   The object is placed in the third quadrant for the third angle projection.  
Object Vs Plane Of Projection To get the first angle projection, the object is placed between the plane of projection and the observer.   To get a third angle projection, the plane of projection is between the observer and the object.  
Assumption On  Plane Of Projection In the first angle projection schema, the plane of projection is assumed to be opaque or non-transparent. The object is placed in front of the planes and each view is pushed through the object which places the vertical plane behind the object and pushes the horizontal plane underneath.   In the third angle projection, the plane of projection is assumed to be transparent and the object is placed below the horizontal plane and behind the vertical plane.  
The Observer In the first angle projection, the orthographic view is projected on a plane located beyond the object and the observer is on the left side of the object and projects the side view on a plane beyond the object.   In third angle projection, the observer is on the right side of the object and the orthographic view is projected on a plane located between the view point and the object.  
The Right View The right side view is projected to the left of the front view and the top view is projected onto the bottom of the front view.   The right view is projected onto the right side of the front view and the top view is projected above the front view.  
Usage First angle projection method is used in Europe, India, Canada and the rest of world as a default projection system.   Third angle projection is used in Australia and United States as a default projection system for industrial designs for product fabrication.  
     

Similarities Between First Angle And Third Angle Projection

  • Both are graphical methods used in engineering drawings.
  • Both are schemas used for multiview projection of three-dimensional objects using a series of two-dimensional drawings.
  • Both methods of orthographic projection result in the same six principal views of the object except the arrangement of views and the state of plane of projection.
  • Both are used to obtain engineering drawings for clarity.

Also Read: Difference Between Orthogonal And Oblique Projection