question: public double exactArea ( ) { S2Point v0 = getVertex ( 0 ) ; S2Point v1 = getVertex ( 1 ) ; S2Point v2 = getVertex ( 2 ) ; S2Point v3 = getVertex ( 3 ) ; return S2 . area ( v0 , v1 , v2 ) + S2 . area ( v0 , v2 , v3 ) ; }
target:  Return the area of this cell as accurately as possible. This method is more expensive but it is accurate to 6 digits of precision even for leaf cells (whose area is approximately 1e-18).