Test Whether A Point Is In A Polygon Or Not

[qetuol]

The Polygon argument can be either a two-dimensional VBA array or a two-dimensional range. If it is a range, assigning that range to a Variant variable converts it to a two-dimensional VBA array so that the rest of the code ends up with the same kind of array as when a real two-dimensional array is inputted. The reason the assignment has to take place within the code is because the coercion to an array does not take place via the argument itself even if that argument is a Variant. So, that line of code makes the overall function flexible enough to handle a real array (assigning such an array to the Variant variable does not change its structure) or a range (because the range gets converted to a real array).




I wanted the function to return either TRUE or FALSE directly in case the function was to be used directly in a MessageBox or to fill a TextBox or any other number of uses besides as the argument to an IF function... the idea being the user can implement the function without having to take special steps to format the output for the occasion. As for why PtInPoly is a Variant and not a Boolean... that was so it could accommodate the error messages when called as a UDF directly on a worksheet.




It was a design decision to help a user not make a mistake. If the user accidentally grabbed the wrong number of rows from a table of coordinates and inputted that too short range of values, the function would alert the user to the error because the last point did not equal the first point... if I made the function close the polygon automatically, it would blindly calculate values and the user would not be aware some of the answers were incorrect... by forcing the user to make sure the polygon closed, he/she could never make a mistake of accidentally inputting to few points.

Rick, thank you for the quick response and clarifications. Anyway, if i want to include each vertex of the polygon only once, not doubling the first and last point, how should i modify the code? is it correct if

For x = LBound(Poly) To UBound(Poly) - 1

is changed to

For x = LBound(Poly) To UBound(Poly) - 2

? thanks

[Rick Rothstein]

Rick, thank you for the quick response and clarifications. Anyway, if i want to include each vertex of the polygon only once, not doubling the first and last point, how should i modify the code? is it correct if

For x = LBound(Poly) To UBound(Poly) - 1

is changed to

For x = LBound(Poly) To UBound(Poly) - 2

? thanks

No, that part of the code would not change... however, you would have to add code to extend the array one additional array element in order to add the first point as a last point so that the For..Next loop would have a last side to test against. Unfortunately, you cannot use ReDim Preserve to expand the array as it is the first element that needs to be increased by one, so you will need to create a new array that is one row bigger than the passed-in array, transfer the elements of the passed-in array to the new array one element at a time and then duplication the first element into the new array's last element and change the array name in the loop to the newly created array's name. Doing this will slow down the function slightly. Personally, forcing the polygon closed before it is passed into the procedure seems more logical to me as the alternative does not seem worth the extra code that would be needed or time necessary to actually encode it. You may feel free to do so if you really think that extra array element to close the polygon is "unsightly" in some way as you have the base code to work from and the above outline of the steps that would be needed.