To complete this a polygon was drawn at the outermost edges of the impact zone .
To complete this a polygon was intersected from the four corners , giving a centre point ( Figure 2 ; end of line A away from centroid location ) .
To complete this a polygon was drawn at the outermost edges of the impact zone and intersected from the four corners , giving a centre point ( Figure 2 ; end of line A away from centroid location ) .