On Dec 6, 2017, at 8:50 AM, Brian Inglis <Brian.Inglis@systematicsw.ab.ca> wrote:
On 2017-12-05 14:29, Guy Harris wrote:
So, for doing a script to do the equivalent of what macOS and iOS do, you'd want more like "get your external IP address, geolocate it, and hand it to a program with a set of shapefiles for tzdb regions". See, for example https://github.com/evansiroky/timezone-boundary-builder (to which http://efele.net/maps/tz/world/ now refers people).
More likely query the underlying geodatabase for the time zone region, often indexed by the minimum bounding rectangle [min x, min y[ - [max x, max y] surrounding the possibly non-convex hull, then resolve muiltiple hits by checking the interior convex polygons contain the coordinate, or equivalent tests.
That's what I meant by "hand it to a program with a set of shapefiles for tzdb regions".