
In Cartesian coordinate system, one deals with a group of mutually perpendicular axes (or planes). Figure 1 shows the 2D Cartesian coordinate system that involves 2 axes (or a plane). The X and Y axes shown in the figure are perpendicular to each other.
Position P shown in Figure 1 can be described as (x, y). In other words, starting from the origin, one can reach P by moving in the direction of the X axis by x and then in the direction of the Y axis by y. x & y are the 2D Cartesian coordinates. A rectangle was drawn for this purpose. For this reason, the Cartesian coordinate system is also called the rectangular coordinate system. Sequence of the movements is not important here. x & y shown in Figure 1 are called the components of the position and they are mutually independent. That is, a motion in the direction of the X axis is independent from a motion in the direction of the Y axis. The 3D Cartesian coordinate system deals with 3 mutually perpendicular straight lines or axes (Figure 2). Again, one can describe the position of point P in terms of three Cartesian coordinates: x, y & z. Starting from the origin, one can reach point P by moving in the direction of the X axis by x, in the direction of the Y axis by y, and in the direction of the Z axis by z. The sequence here, again, does not matter.
Note in Figure 2 that the Z axis is aligned vertically. This is the traditional 3D Cartesian coordinate system and will be used consistently throughout this website. Those who are accustomed to the ISB convention, in which the Y axis is aligned vertically, should switch the axes properly.

© YoungHoo Kwon, 1998 