Projection Of Points 5gt1b

PROJECTIONS OF POINTS

DEVARAJAN K

ORTHOGRAPHIC PROJECTION • When the projectors are parallel to each other and also perpendicular to the plane, the projection is called orthographic projection • Step:1 Imagine that a person looks at the block (Fig:-1) from a theoretically infinite distance, so that the rays of sight from his eyes are parallel to one another and perpendicular to the front surface F. The view of the block will be shaded figure, showing the front surface of the object in its true shape and proportion

ORTHOGRAPHIC PROJECTION • •

•

Step:2 If these rays of sight are extended further to meet perpendicularly a vertical plane (marked V.P) set up behind the block Step:3 The points at which they meet the plane are ed in proper sequence, the resulting figure (marked E) will also be exactly similar to the front surface and this is known as an elevation or front view. The figure is the projection of the block. The lines from the block to the plane are the projectors. The projection is shown in separately shown, It shows only two dimensions of the block ( width and height). It does not show the thickness. Thus, we find that only one projection is insufficient for complete description of the block

ORTHOGRAPHIC PROJECTIONS • Orthographic projection is a means of representing a three-dimensional (3D) object in two dimensions (2D) • Orthographic Projection is a method of representing a three dimensional object on paper using several two dimensional views • It is the international language of Engineers and Designers

X-Y is the reference line (Intersection of HP and VP)

To find solution of problems based on projections we need to rotate H.P. (Horizontal Plane) in clockwise direction to 90º After this rotation of H.P. it will become parallel to V.P. See fig below.

FIRST ANGLE VS. THIRD ANGLE PROJECTION

FIRST ANGLE VS. THIRD ANGLE PROJECTION

PROJECTIONS OF POINTS A point may be situated, in space, in any one of the four quadrants formed by the two principal planes of projection or may lie in any one or both of them. Its projections are obtained by extending projectors perpendicular to the planes. One of the planes is then rotated so that the first and third quadrants are opened out. The projections are shown on a flat surface in their respective positions either above or below or in xy.

PROJECTIONS OF POINTS Four Cases: 1. The point is situated in the first quadrant. 2. The point is situated in the second quadrant. 3. The point is situated in the third quadrant. 4. The point is situated in the fourth quadrant.

A POINT IS SITUATED IN FIRST QUADRANT

h

a’

y

o d

x

a

A POINT IS SITUATED IN SECOND QUADRANT

b

x

o

d

h

b’ y

A POINT IS SITUATED IN THIRD QUADRANT

d

c

y

o h

x

c’

A POINT IS SITUATED IN FOURTH QUADRANT

o

y h d

x

e’ e

First quadrant --- Above HP and in front of VP Second quadrant --- Above HP and behind VP Third quadrant --- Below HP and behind VP Fourth quadrant --- Below HP and in front of VP

Draw the projections for the below points. Take a single reference line. The distance between the projectors is 40mm. a) Point ‘A’ is 20mm above HP and 30mm in front of VP. b) Point ‘B’ is 20mm below HP and 40mm behind VP. c) Point ‘P’ is 10mm above HP and 30mm Behind VP. d) Point ‘C’ is 45mm below HP and 35mm in front of VP.

PROJECTIONS OF POINTS A point P is 15 mm above the H.P. and 20 mm in front of the V.P. Another point Q is 25 mm behind the V.P. and 40 mm below the H.P. Draw projections of P and Q keeping the distance between their projectors equal to 90 mm. Draw the straight lines ing (i) their top views and (ii) their front views.

PROJECTIONS OF POINTS

PROJECTIONS OF POINTS

The two points A and B are in the H.P. The point A is 30 mm in front of the V.P., while B is behind the V.P. The distance between their projectors is 75 mm and the line ing their top views makes an angle of 450 with xy. Find the distance of the point B from the V.P.

PROJECTIONS OF POINTS

PROJECTIONS OF POINTS A point P is 20 mm below H.P. and lies in the third quadrant. Its shortest distance from xy is 40 mm. Draw its projections.

PROJECTIONS OF POINTS

PROJECTIONS OF POINTS A point A is situated in the first quadrant. Its shortest distance from the intersection point of H.P., V.P. and auxiliary plane is 60 mm and it is equidistant from the principal planes. Draw the projections of the point and determine its distance from the principal planes.

PROJECTIONS OF POINTS

PROJECTIONS OF POINTS

A point 30 mm above xy line is the plan-view of two points P and Q. The elevation of P is 45 mm above the H.P. while that of the point Q is 35 mm below the H.P. Draw the projections of the points and state their position with reference to the principal planes and the quadrant in which they lie.

PROJECTIONS OF POINTS