Detecting lines which pass close to points, lines or polygons #2

[mikemcc]

I started a thread of the same name on Sept 17 at:
http://groups.google.com/group/kml-support-third-party-applications/browse_thread/thread/08048dff83ef4de9

Frankv provided excellent help and offered to code in php but sadly
the thread has time-expired, so I can't post to it.

Frankv, if you are still interested, please email me at mike at around-
the-world.co.uk. I need to know:
1. Whether a line segment intersects a circle
2. Whether a line segment intersects a polygon
3. The length of the line within the circle / polygon.

The geometry is anywhere on the surface of the earth. Line segments
can be as much as 1,300 nautical miles (or km, I can't quite remember
which just now, but not short anyway).

Data is held on MySql 5.0.77.

Thanks, Mike McC