Projection of Points

A  POINT 
The position of a point in engineering drawing is defined with respect to its distance from the three principle planes i.e., with respect to the VP, HP, & PP.
The point is assumed to be in the respective quadrant shown in figure.  The point at which the line of sight (line of sight is normal to the respective plane of projection)  intersects the three planes are obtained.  The horizontal plane and the side planes are rotated so such that they lie on the plane containing the vertical plane. The direction of rotation of the horizontal plane is shown in figure 

The relative positions of projection planes and the quadrants

The direction of rotation of the Horizontal plane.

Conventions used while drawing the projections of points

With respect to the 1^st angle projection of point “P’ shown in figure 2,

·        Top views are represented by only small letters eg. p .

·        Their front views are conventionally represented by small letters with dashes eg. p΄

·        Profile or side views are represented by small letters with double dashes eg. p΄΄

·        Projectors are shown as thin lines.

·        The line of intersection of HP and VP is denoted as X-Y.

·        The line of intersection of VP and PP is denoted as X1-Y1

Showing the three planes and the projectionof the point P after the planes have been rotated on to the vertical plane.

Point in the First quadrant

Projection of the point “P” on to the three projection planes after the planes are partially rotated.

Figure 3 shown the projections of a point P which is  40 mm in front of VP, 50 mm above HP, 30 mm in front of left profile plane (PP)

Projection of the point “P” on to the three projection planes before the planes are rotated.

The procedure of drawing the three views of the point “P” is shown in figure-4.

·        Draw a thin horizontal line, XY, to represent the line of intersection of HP and VP.

·        Draw X₁Y₁ line to represent the line of intersection of VP and PP.

·        Draw the Top View (p).

·        Draw the projector line

·        Draw the Front View (p΄) .

·        To project the right view on the left PP, draw a horizontal projector through p to intersect the 45 degree line at m. Through m draw a vertical projector to intersect the horizontal projector drawn through p΄ at p΄΄.

·        p΄΄ is the right view of point P

First angle multi-view drawing of the point “P”