[Alan Anderson]

Both polar and cartesian varieties have a "rotation" parameter. That determines how the robot spins around its center of rotation.

The difference is in how the translational motion is specified. Cartesian control has separate X (left/right) and Y (forward/backward) parameters. Polar control uses a vector with a direction and a magnitude, saying how fast to move in the specified direction. Polar also has an optional parameter that can make the robot move in absolute field directions instead of relative to the robot's "front" side, if you implement a gyro properly.