main/src/georegression/metric/Intersection2D_F64.java
public static double intersectionArea( Rectangle2D_F64 a , Rectangle2D_F64 b ) {
		if( !intersects(a,b) )
			return 0;

		double x0 = Math.max(a.p0.x,b.p0.x);
		double x1 = Math.min(a.p1.x,b.p1.x);
		double y0 = Math.max(a.p0.y,b.p0.y);
		double y1 = Math.min(a.p1.y,b.p1.y);

		return (x1-x0)*(y1-y0);
	}
public static double intersectionArea( Rectangle2D_F64 a , Rectangle2D_F64 b ) {
		if( !intersects(a,b) )
			return 0;

		double x0 = Math.max(a.p0.x,b.p0.x);
		double x1 = Math.min(a.p1.x,b.p1.x);
		double y0 = Math.max(a.p0.y,b.p0.y);
		double y1 = Math.min(a.p1.y,b.p1.y);

		return (x1-x0)*(y1-y0);
	}
Returns the area of the intersection of two rectangles.

@param a Rectangle
@param b Rectangle
@return area of intersection