Understanding the coordinates system

In the last section while working on the size of the graphical shapes, we understood that when a square object with size 4, it will cover the whole GEM window. In the polygon and curve examples, we learned that each point in the GEM window corresponds to a point in three-dimensional space.

The GEM window is a two-dimensional projection plane of a three-dimensional space. The origin (0, 0, 0) is the center of the window. The horizontal axis is the x axis. Toward the right-hand side is the increasing value of x. The vertical axis is the y axis. Moving upward increases the value of y. For the z axis, you have to imagine a line moving from the center of the GEM window toward your eyes:

If we consider all the points with z value equal to zero, it will form a flat surface parallel to the GEM window. On this surface, when we move from the left-hand margin to right-hand margin, the x value changes from -4 to 4. When we move from the bottom margin to the top margin, the y value changes from -4 to 4. The measurement is due to the default settings of the GEM window view properties and is independent of the window's dimension in pixels.