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Figure 1.5 'Can you find the answer ?' handout

Figure 1.6 Geometrical optical illusions may not understand the theories, the eye/brain sees lines of different length. This is another example of the fact that what the eye sees, even in two dimensions, is not necessarily reality.

All the examples of visual illusions in Figures 1.2 to 1.6 illustrate the complexities involved in firstly representing three-dimensional information in two-dimensional space and secondly making sure the interpretation of the two-dimensional space is correct. It is for these reasons that the fathers of engineering drawing decided that, in orthographic projection, only two-dimensional views would be taken which are projected from one another and things like perspective would be ignored. In this way the 'noise' which could creep into the communication sequence in Figure 1.1 would be reduced to a minimum. The two basic sets of rules of orthographic engineering drawing are based on what is called 'first angle' or 'third angle' projection. The word 'ortho' means right or correct.

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