Following some suggestions from Mike Seymour I have modified my polyline intersection function, and added a new version. The changes are:

• The data ranges for the new function, IP4(), are entered as four separate ranges, so the X and Y values do not need to be in adjacent columns.
• For both IP() and IP4() the data may now be arranged in rows, rather than columns.  If the data ranges have more than 2 columns for IP(), or more than 1 column for IP4(), it is assumed that the data is arranged row-wise.

The new spreadsheet may be downloaded from: IP.zip

The spreadsheet also includes a number of geometric and interpolation functions.  As usual, full open-source code is included n the download.  See https://newtonexcelbach.wordpress.com/2008/08/10/intersections-interpolations-and-rotations/ for a full list.