Formula for calculating irregular plot area based on point coordinates

for the number of points, I is any one point, X and Y are horizontal ordinate, ∑ is the sum. For example, the coordinates of the three vertices of a triangle in a planar Cartesian coordinate system are (a, b), (C,d), (e,f), then the area of the triangle is:0.5a (d-f) +0.5c (f-b) +0.5e ( b-d)

You can also change the formula X to Y,y for x, the same reason.

From: http://ete1314.blog.163.com/blog/static/162561137201031894053871/

Formula for calculating irregular plot area based on point coordinates