rough estimate of the time offset from GMT from latitude longitude

Question

Is there a way to estimate the offset from GMT (or time zone) from a latitude/longitude? I\'ve seen geonames, but this would need to work long term and we don\'t really want to

Answer 1

offset = direction * longitude * 24 / 360

where direction is 1 for east, -1 for west, and longitude is in (-180,180)