Date: 06/05/99 at 11:20:14 From: Alessandro Pagani Subject: Area of irregular nonconvex polygon I'm a student of the Politecnico di Milano (Italy) as an environmental engineer. I need a method to calculate the area of an irregular polygon in a Visual Basic program. On your website, I've read about a formula to be used in a program when I have the lengths of all the sides and some of the angles. My problem is different: I have all the spatial topographic coordinates of the points of a drainage area that may be nonconvex. Can you help me? Thanks.
Date: 06/06/99 at 08:25:42 From: Doctor Jerry Subject: Re: Area of irregular nonconvex polygon Hello Alessandro, You can use the "surveyor's formula." It gives the area of any planar polygon. If the vertices are (x1,y1), (x2,y2), ..., (xn,yy), then A = (1/2)[Det(x1,x2,y1,y2)+Det(x2,x3,y2,y3)+ ... +Det(xn,x1,yn,y1)], where Det(a,b,c,d) = a*d-b*c. - Doctor Jerry, The Math Forum http://mathforum.org/dr.math/
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