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Orthographic Projections

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A three dimensional sketch of an object to be manufactured doesn’t always gives a clear idea about the exact construction. The artisan or craftsman needs constructional details which can be better explained in the Orthographic Projections. Orthogonal means ‘Perpendicular’, The object is observed with the viewer’s eye sight at 90 degrees to a face of the object shown in fig. 11.1

In First Angle Projection we place our object in the First Quadrant and in Third Angle Projection the Object is placed in the Third Quadrant. (See fig 11.2). It is consider as if the object is placed in a glass box with three planes of the object being parallel to the glass box. The image (or shadow or reflections) received on the three planes, collectively are called as ‘orthographic projections’. 

When we draw an Orthographic view of the front of an object it is called an ELEVATION. When we draw an Orthographic view of the top of an object it is called a PLAN. When we draw an Orthographic view of one side of an object it is called an END ELEVATION. If an object is very complicated then you can draw an End Elevation of the left and right hand side. Observe following object and their orthographic projections: