main/src/georegression/geometry/UtilCircle2D_F64.java
public static double evaluate( double x , double y, Circle2D_F64 circle ) {
		x -= circle.center.x;
		y -= circle.center.y;

		return x*x + y*y - circle.radius*circle.radius;

	}
public static double evaluate( double x , double y, Circle2D_F64 circle ) {
		x -= circle.center.x;
		y -= circle.center.y;

		return x*x + y*y - circle.radius*circle.radius;

	}
Computes (x-x_c)**2 + (y-y_c)**2 - r. If (x,y) lies on the circle then it should be 0.
@param x x-coordinate of a point
@param y y-coordinate of a point
@param circle circle
@return Result of the equation