# Projections

Topics: Parallel projection, Graphical projections, Orthographic projection Pages: 3 (594 words) Published: January 11, 2013
PROJECTIONS
The engineering drawing is a set of conventions for the representation of object with technical purposes (design, production).For that, we use graphical projections. GRAPHICAL PROJECTION:
The production of a two dimensional image of a three dimensional object. HISTORY OF PROJECTIONS:
Throughout human history we have used pictures to convey ideas, express ourselves, present information, etc. Basically we have used pictures to communicate. The difference in drawings across time and countries was a problem that faced engineers, designers, builders, architects, etc. Throughout history. This was a problem that faced gaspard monge when he started as an engineer in the french military. He devised a system called orthographic projection, that could be used to communicate an object to anyone across the world. It was quickly adopted by army engineers. BASIC REQUIREMENTS OF A DRAWING (OTHER THAN INSTRUMENTS):

An object
An observer
A plane
TWO METHODS TO DRAW EXACT DIMENSIONS OF AN OBJECT:
Place the object on a paper and trace its outline.
Place a paper on the object and trace its shadow.
PROJECTIONS IN USE:
Similar to the above practical methods, there are two types of projections are only used in engineering drawings.

FIRST ANGLE PROJECTION:
It is the drawing of an object by projecting the object to a plane of projection behind the object. Thus the object is placed in between the observer and the plane of projection. THIRD ANGLE PROJECTION:

It is the drawing of an object by projecting the object to a plane of projection in front of the object. Thus the plane of projection is placed in between the object and the observer. DIFFERENCE BETWEEN 1ST & 3RD ANGLE PROJECTIONS:

The main difference is only the sequences/order of the object placed in the quadrants. The denotation of first angle or third angle is purely based on quadrants. Each quadrant is split into 90° to...

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