ORTHOGRAPHIC PROJECTION

4.1 Introduction

In chapter 3, you learnt about three-dimensional objects and also drew them in oblique and isometric projections. Do you recall that in each of these projections the front, plan and end views were all represented in one drawing? Suppose you wanted a detailed drawing of the front, plan and end views in two dimensions, what would you do?

Orthographic projection is another way of representing a three-dimensional object in two-dimensions in order to represent the object’s length, height and width. The arrangement of these three views can be represented in either 1 or 3d angle projection. Architects use orthographic projection to make detailed drawings of house plans.

In this chapter, you will interpret and transform three-dimensional (3D) into

two-dimensional (2D) views (orthographic projection).

4.2 Principles used in Orthographic Projection

Principles used in orthographic projection are guidelines you can use when drawing in orthographic projection. You can draw three views of the object, that is; the Front, Plan, and End as you see them in three separate directions and then represent them in imaginary planes. In essence, the Vertical Plane (VP), the Horizontal Plane (HP) or the sides of the Vertical Plane (SVP).

4.3 Presentations of Drawings

Before you carry out drawing in orthographic projection first interpret the given drawing of the object to identify the front, plan and elevation. You can make a sketch of the object and shade areas which can give you the required views. Go on and draw the views in Figure 4.7 and Figure 4.8.

Activity 4.2 Applying principles of orthographic projection to draw different views of objects

What you need: 2H pencil, ruler, pair of compasses, dividers, eraser, T-square, board, clips and drawings of objects

What to do: In pairs, carry out this activity.

1. Draw the following shaped blocks in orthographic projection Figure 4.10 to Figure 4.14.

2. Make sure your drawing instruments and equipment are in good condition.
3. Endeavour to draw accurately.

4.4 Orthographic Symbols

A symbol is the shortest and quickest method you can use to convey your information. In orthographic projection, you can use symbols for interpreting the type of orthographic projection. There are two main types of symbols you can use, namely, First Angle symbol and Third Angle symbol.

Example

Drawing a block in:

a) First Angle projection Figure 4.17

b) Third Angle projection Figure 4.17

If you compare the two drawings in the orthographic projection in First Angle and Third Angle, you will notice some differences in the positioning

When you are drawing orthographic views, remember to:

include dimensions

use projection lines

include the name of the object you are drawing

the projection you have used.

Activity 4.3 Using orthographic symbols to interpret and draw orthographic views

What you need: Drawing instruments and equipment

What to do: In pairs carry out this activity

1. Draw the following objects in orthographic projection (Figure 4.18 to

Figure 4.21):

a) A front elevation

b) A plan

c) An end as indicated by the arrow.

2. Add six important dimensions to your drawing.
3. Indicate the projection you have used at the top right corner of your paper.

After studying this chapter, you should be able to use orthographic projection while designing various items for the community. Look at the following example of a table.