Polygon Area
by THavamani[ Edit ] 2013-03-16 12:56:08
X, Y are=Arrays of the x and y coordinates of the vertices, traced in a clockwise direction, starting at any vertex. If you trace them counterclockwise, the result will be correct but have a negative sign.
numPoints=The number of vertices
Returns =the area of the polygon
<u>The algorithm, in JavaScript:</u>
function polygonArea(X, Y, numPoints)
{
area = 0; // Accumulates area in the loop
j = numPoints-1; // The last vertex is the 'previous' one to the first
for (i=0; i<numPoints; i++)
{ area = area + (X[j]+X[i]) * (Y[j]-Y[i]);
j = i; //j is previous vertex to i
}
return area/2;
}
