What Is Projection And Its Types

 What Is Projection ?

Any kind of representation of an object on a paper, screen or similar surface by drawing is called projection of the part the parallel rays that are used for construction the views are called projectors.

Types Of Projection 

1.Pictorial Projection-: The projection in which the description of the object is completely understood in one view is known as pictorial projection. they have the advantage of conveying in immediate impression of the general shape and details of the object, but not its true dimension or sizes. types of pictorial projection are as following.

• Perspective Projection 
• Isometric Projection 
• Oblique Projection 

2. Orthographic Projection-: Ortho means right angle and orthographic means right angled drawing, when the projectors are perpendicular to the pane on which the projection is obtained, its known as the orthographic projection. types of orthographic projection are as following. 

• 1st angle projection 
• 3rd angle projection 

Obtaining the projection on the drawing sheet  

                                                                                Fig.1

It is convention to rotate the H.P through 90 degree in the clockwise direction about XY line so that is lies in the extension of VP as shown in fig 1. The two projections front view and top view may be drawn on the two dimension drawing sheet as shown in fig 1

Those all details regarding the shape and size, viz length (L), height (H), and breadth (B) of any object may be represented by means of orthographic projection i.e front view and top view 

The VP and HP are called as the principal planes of projection or reference planes. they are always transparent and at right angles to each other. the projection on VP designated as front view and the projection on HP as top view. 

Quadrants 

Fig.2

When the planes of projection are extended their line of intersection, they form four quadrants. these quadrants are numbered as 1st, 2nd, 3rd, and 4th in clockwise direction when rotated about reference line XY as shown in fig 2 

In the fig 3. the object is in the first quadrant and the projection obtained are first angle projection i.e the object a lies in between the observer and the planes of projection. front view shows the length (l), and height (H) of the object, and top view shows the length(l) and the breadth (b) of it.

Fig.3

The object may be situated in any one of four quadrants, its position relative to the planes being describe as in front of VP and above HP in the first quadrant and so on.

Fig 3, shows the two principle planes HP and VP and another auxiliary vertical plane. AVP is perpendicular to both VP and hp.

Front view is drawn by projecting the object in the VP top view is drawn by projecting the object on the hp. the projection on the AVP as seen from the left of the object and drawn on the right of the front view, is called left side view.

What is 1st angle and 3rd angle projection 

1st angle projection-: When the object is situated in first quadrant, that is , in front of vp and above hp, the projection obtained on these planes is called first angle projection.

1. The object is imagined to be in first quadrant 
2. The object is lies between the observer and plane of projection 
3. The plane of projection is assumed to be non transparent 
4. When the view are drawn in their relative position top view comes below front view, right side view drawn to the left side of elevation 
5. Symbol of 1st angle projection 

3rd angle projection-: In this, the object is situated in third quadrant. the planes of projection lie between the object and the observer. the front view comes below the xy line and the top view about it.

1. The object is imagined to be in third quadrant 
2. The plane of projection lies between the observer and object 
3. The plane of projection is assumed to be transparent.
4. When view are drawn in their relative position top view comes above front view, right side view drawn to the right side of elevation.
5. Symbol of 3rd angle projection 

A Textbook of Engineering Drawing (In First Angle Projection)

This book includes Geometrical Drawing & Computer Aided Drafting in First Angle Projection.Useful for the students of B.E./B.Tech for different Technological Universities of India.According to the Bureau of Indian Standards (BIS) SP:461988 amd IS:6961972.

Covers all the topics of engineering drawing with simple explanation.

Also includes chapters on Geometrical drawing and Computer Aided Drafting.More than 1500 illustrations with proper explanations. Numerous Solved problems, questions for SelfExamination and problems for practice are also given.

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