Here's my racecourse. It has the radius r, which you can set.

So now I want to make a more interesting course, a cyclic course, a racecourse.

The way I'd like to define this racecourse is through a half cycle where we use r, same half cycle over here, and the stretches in between I want to be 2r long.

I want you to program it such that the initial car is stationed right over here, pointed upwards, and then it drives onto the racecourse like this, all the way around infinitely often.

On the left side, if I'm on the left side of the racecourse, as defined that x is smaller to radius, then my crosstrack_error is defined by the distance to the circle, centered at radius comma radius minus the radius itself.