DIFFERENCE BETWEEN FIRST ANGLE AND THIRD ANGLE PROJECTION EXPLAINED !!

Orthographic projection  is a means of representing a three-dimensional object in two dimensions. It is a form of parallel projection, where all the projection lines are orthogonal to the projection plane, resulting in every plane of the scene appearing in affine transformation on the viewing surface. A lens providing an orthographic projection is known as an (object space) telecentric lens.

There are two types of drawing in orthographic , First Angle and Third Angle. They differ only in the position of the plan, front and side views.

First Angle Projection :

1.)In first angle projection, that object is assumed to be in the first quadrant. Hence, the top view is projected below, i.e. to the x-z plane - which lies below the object.

2.)The object is assumed to be positioned in between the projection planes and the observer.

3.)The views are obtained by projecting the images on the respective planes.

4.)First Angle Projection is commonly used in all countries other than United States. The Indian Standard Institution (ISI) recommend the use of First Angle Projection method now in all the institutions.

5.)In first angle projection right view come in left of front view and top view come at the bottom of front view.

Fig : First Angle Projection

Third Angle Projection:

1.)In the third angle projection method, the object is assumed to be in the third quadrant. i.e. vertical Plane is in front of the object and the Horizontal Plane is above the object.

2.)For the third angle projection plane of projection is placed between the object and observer.

3.)Third Angle Projection is commonly used in United States of America.

4.)In third angle projection right view come on right side of front view and top view comes at the top of front view.

Fig:Third Angle Projection

Major differences between first angle and third angle projection:

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