Test Whether A Point Is In A Polygon Or Not

[Rick Rothstein]

Hi Rick, I am trying to use your function (PtInPoly) inside a function i've made (APPROACH). It's inside an If;

Function APPROACH(P1 As Range, x1 As Double, y1 As Double) As Double

Dim A1(3, 3) As Double
Dim A2(5, 2) As Double

For i = 1 To 5 Step 2
A1(1, 1) = P1(i, 1)
A1(1, 2) = P1(i, 2)
A1(1, 3) = P1(i, 3)
A1(2, 1) = P1(i + 1, 1)
A1(2, 2) = P1(i + 1, 2)
A1(2, 3) = P1(i + 1, 3)
A1(3, 1) = P1(i + 2, 1)
A1(3, 2) = P1(i + 2, 2)
A1(3, 3) = P1(i + 2, 3)

A2(1, 1) = P1(i, 1)
A2(1, 2) = P1(i, 2)
A2(2, 1) = P1(i + 1, 1)
A2(2, 2) = P1(i + 1, 2)
A2(3, 1) = P1(i + 3, 1)
A2(3, 2) = P1(i + 3, 2)
A2(4, 1) = P1(i + 2, 1)
A2(4, 2) = P1(i + 2, 2)
A2(5, 1) = P1(i, 1)
A2(5, 2) = P1(i, 2)

If PtInPoly(x1, y1, A2) = 0 Then
    APPROACH = AltXY(A1, x1, y1)
    Exit For
End If
Next i

End Function

I want the function, in case the point (x1,y1) is INSIDE the polygon, to apply function AltXY (If PtInPoly(x1, y1, A2) = 0 Then...) and if not, check for other areas but for some reason its giving me the wrong result. AltXY is not badly written, as if I wanted it to give me APPROACH = 10, it still keeps giving me zeros but I don't understand why. Any help is appreciated

You did not supply an x1,y1 point that fails to work so that I could test it out; however, I am suspicious of your A1 array declaration (probably your A2 array's declaration as well). You have the A1 array declared as...

Dim A1(3, 3) As Double

but then you start filling it at element number 1. Unless you are using Option Base 1, your declaration set the lower bound for the array at 0, not 1 and that might be screwing up the calculations in my code (not sure, but I think it would). Try changing your declaration to this and see if that solves the problem...

Dim A1(1 To 3, 1 To 3) As Double

This declaration set the lower bound to 1, not 0. While I don't know if it matters to your AltXY function or not, but for consistency, I would change the declaration for the A2 array in a similar way.