30th April 2020, Period 3, Class 11, Engineering Graphics - Projection of a point - 1

Dear Students,

Good Morning and a warm welcome to today's class.

It feels really nice to meet up for yet another class this morning.

We will learn about Orthographic projection in today's class.

Orthographic Projection

The word Orthographic consists of two words 'Ortho' and 'Graphic'. 'Ortho' means 'right angles' and 'graphic' means drawing. Therefore, orthographic projection is a drawing in which the line of sight falls perpendicularly on the Planes of projection.

Projectors

The lines of sight or rays that fall go past the object and falling on the so called 'screens'.

Projection

Projection is the representation of the shape (something similar to the shadow) of the object on a plane (or the screen). If straight lines are drawn from various pointson the contour of the object to meet the plane (screen) the figure so obtained on the plane id called as the projection of he object.

Planes of Projection 

The screen referred above is actually the plane of projection that hosts the figure (or the shadow) of the object.

Refer to Fig 1 below. The object is placed in the first quadrant and its shadow falls on the horizontal and the vertical planes.   







Fig 1: Planes of projection or Principal planes


Exercise - Projection of a point

Q 1. A point is placed 50 mm in front of the VP and 20 mm above the HP. Draw its projections.