find area of polygon with coordinates

find area of any polygon with coordinates

To find area of any polygon for the given coordinates, use the following concept/algorithm:
* First find "(x1*y2)-(x2*y1)".
* Get the sum of all the coordinates given to form a polygon.
* Divide the total sum by 2.

For eg,

   A     B     C     D     A    

 (2,3),(4,5),(6,7),(8,9),(2,3)

 cal1 = (2*5)-(3*4)

 cal2 = (4*7)-(5*6)

 cal3 = (6*9)-(7*8 )

 cal4 = (8*3)-(9*2)

 Sum = cal1+cal2+cal3+Cal4

 Total = Sum/2