Generating contours from NASA SRTM data

Nick Whitelegg said:

Further to the Freemap thread, I'm interested in generating contours
for Freemap from raw NASA SRTM data. I can think of one or two
possible ways of doing this from logically analysing the problem
alone, but there's bound to be some maths magic somewhere which does
it quickly and efficiently.

Can anyone recommend any good online articles on how to do this?

A very quick search among free-as-in-beer software suggests GNUPlot as a
possibility. It will generate a contour map given a regular XY grid of data
points though I'm not sure about interpolation, nor how practical it would
be for the volume of data needed for a map.
--
Dave

Nick,

This is not a trivial exercise, try a search on 'CONREC algorithm'.
You'll need to think very carefully how you interpolate the heights from
the SRTM data in order to get reasonable results.

--
Andrew Whaley, author of :-

Trailgauge - Shareware 3D GPS Mapping Software
Free Download from http://www.trailgauge.com