What is 3rd-angle projection?

Third-angle projection is a method of orthographic projection, which is a technique for portraying a 3D design using a series of 2D views. The 3rd-angle projection is where the 3D object is seen to be in the 3rd quadrant. It is positioned below and behind the viewing planes; the planes are transparent, and each view is pulled onto the plane closest to it. The front plane of projection is seen to be between the observer and the object.

The images below show the projection of the object on a 3D box surrounding the object. The box is then gradually unfolded to then present a series of 2D views in the 3rd-angle projection as viewed by the observer.

The following demo shows this in motion:

The views below show the same object in first an Isometric 3D view, then the corresponding 2D 3rd Angle projection views in the specific alignment. The annotations on the 2D views show how the top and left views are aligned to the front view.

• The front view, is a drawing of the block, as if you are looking directly at the front of the object.
• The side view, is a drawing of the block, when it has been rotated so that one of its sides is now directly in view.
• The plan view, is a ‘birds eye’ view, from above.

The 3rd-angle projection symbol shows the orientation of a cone in the 3rd-angle projection.