Three-dimensional co-ordinate geometry
Before we lead on to a study of the graphical display of objects in three-dimensional space, we first have to come to terms with the three-dimensional Cartesian co-ordinate geometry and introduce some useful procedures for manipulating objects in three-dimensional space. (For further reading we recommend books by Cohn (1961) and McCrae (1953).) As with two-dimensional space, we arbitrarily fix a point in the space, named the co-ordinate origin (origin for short). We then imagine three mutually perpendicular lines through this point, each line extending to infinity in both directions. These are the x-axis, y-axis and z-axis. Each axis is thought to have a positive and negative half, both starting at the origin — that is, distances measured from the origin along the axis are positive on one side and negative on the other.
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