Orthographic projection

In orthographic projection, the front face is always parallel to the picture frame and the projectors are perpendicular to the picture frame (see Figure 2.9). This means that one only ever sees the true front face that is a 2D view of the object. The receding faces are therefore not seen. This is the same as on an oblique projection but with the projectors perpendicular rather than at an angle. The other faces can also be viewed if the object is rotated through 90 degree .There will be six such orthographic views. These are stand-alone views but if the object is to be 'reassembled' from these six views there must be a law that defines how they are related. In engineering drawing there are two laws, these are first or third angle projection. In both cases, the views are the same; the only thing that differs is the position of the views with respect to each other. The most common type of projection is third angle projection.
Engineering Drawing for Manufacture by Brian Griffiths Publisher:
Elsevier Science &
Technology Books