Polar Coordinate Systems - 3D Math Primer for Graphics and Game Development - page 193

Step 2. Now move forward from the origin a distance of r units. You have
arrived at the point described by the polar coordinates (r,θ).

This process is shown in Figure 7.2.

Figure 7.2. Locating a point using 2D polar coordinates

In summary, r defines the dis-
tance from the point to the origin,
and θ defines the direction of the
point from the origin. Figure 7.3
shows several points and their po-
lar coordinates. You should study
this figure until you are convinced
that you know how it works.
You might have noticed that
the diagrams of polar coordinate
spaces contain grid lines, but that
these grid lines are slightly dif-
ferent from the grid lines used
in diagrams of Cartesian coordi-
nate systems. Each grid line in
a Cartesian coordinate system is
composed of points with the same
value for one of the coordinates. A
vertical line is composed of points
that all have the same x-coordinate, and a horizontal line is composed of

Figure 7.3
Example points labeled with 2D polar
coordinates