Intro to Engineering Graphics

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Drawing is a graphical representation of a thought, an idea, a concept, a structure or an object which actually or potentially exists in life and could be done using freehand, mechanical or computer methods. It can also be defined as a graphical language in engineering application that use lines to represent the surfaces, edges and contours of objects. It can also be referred to as drafting. The drawing itself is

A way of communicating all necessary information about abstraction ,such as an idea or a concept •A graphic representation of some real entity, such as machine part, a house, a tool. Types of drawing includes

Artistic drawing
Technical drawing
Rendering or illustration drawing
ARTISTIC DRAWING: it ranges in scope from the simplest line drawing to the most famous paintings. Regardless of their status or complexity, they are used to express the feelings, beliefs, philosophies or abstract ideas of the artist. Hence in order to understand it, you must understand the artist. TECHNICAL DRAWING: it is a means of clearly and concisely communicating all of the information necessary to transform an idea or a concept to reality. It can also be defined as an act or discipline of composing plans that virtually communicate how something functions or how it is to be constructed. Therefore, a technical drawing often contains more than a graphical representation of its subject. It also contains dimensions notes and specification. RENDERING OR ILLUSTRATIONS: they are neither completely technical nor artistic, they combine elements from both hence are referred to as the third type of drawing. They are technical in that they are drawn with mechanical instrument or on a computer-aided drafting system and they contain some degree of technical information. However, they are also artistic in that they attempt to convey a mood, a status, or other abstract, non technical feelings. Projection is a protocol by which an image of a three-dimensional object is projected onto a planar surface without the aid of mathematical calculation, used in technical drawing. The projection is achieved by the use of imaginary "projectors". The projected, mental image becomes the technician’s vision of the desired, finished picture. By following the protocol the technician may produce the envisioned picture on a planar surface such as drawing paper. Types of projection

Parallel projection
Perspective projection
PARALLEL PROJECTION: In parallel projection, the lines of sight from the object to the projection plane are parallel to each other. It preserves the true relationships of an object’s features and edges. It is the basis of most engineering and technical graphics. It is divided into two types orthographic and oblique projection. PERSPECTIVE PROJECTION: it is a type of projection where three dimensional objects are not projected along parallel lines, but along lines emerging from a single point. This has the effect that distant objects appear smaller than nearer objects. It also means that lines which are parallel in nature appear to intersect in the projected image, for example if railways are pictured with perspective projection, they appear to converge towards a single point, called vanishing point. It represents 3 dimensional objects on 2 dimensional media. Perspective projection is not used by engineer for manufacturing of parts, because it is difficult to create and it does not reveal exact shape and size. In OBLIQUE PROJECTIONS the parallel projection rays are not perpendicular to the viewing plane as with orthographic projection, but strike the projection plane at an angle other than ninety degrees. In an oblique pictorial drawing, the displayed angles among the axes as well as the foreshortening factors (scale) are arbitrary. The distortion created thereby is usually attenuated by aligning one plane of the imaged object to be parallel with the plane of projection thereby creating a true shape, full-size image...
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