how to find area of polygon with coordinates in javascript
Algorithm to find the area of a polygon
If you know the coordinates of the vertices of a polygon, this algorithm can be used to find the area.
Parameters
X, Y 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
The algorithm, in JavaScript:
function polygonArea(X, Y, numPoints)
{
area = 0; // Accumulates area
j = numPoints-1;
for (i=0; i<numPoints; i++)
{ area += (X[j]+X[i]) * (Y[j]-Y[i]);
j = i; //j is previous vertex to i
}
return area/2;
}