Shoelace formula for polygonal area: Difference between revisions

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@@ Line 1,277: / Line 1,277: @@
 Public Function ShoelaceArea(x() As Double, y() As Double) As Double
-Dim i As Long
+Dim i As Long, j As Long
 Dim Area As Double
-  For i = 1 To UBound(x()) - LBound(x())
+  j = UBound(x())
-    Area = Area + (y(i - 1) + y(i)) * (x(i - 1) - x(i))
+  For i = LBound(x()) To UBound(x())
+    Area = Area + (y(j) + y(i)) * (x(j) - x(i))
+    j = i
   Next i
-  'last vertex = first vertex:
-  Area = Area + (y(i - 1) + y(0)) * (x(i - 1) - x(0))
   ShoelaceArea = Abs(Area) / 2
 End Function