[R] time zones from longitude, latitude, and date

[David Winsemius]

On Sep 21, 2013, at 3:13 AM, Prof Brian Ripley wrote:

> On 21/09/2013 08:17, Gabor Grothendieck wrote:
>> On Fri, Sep 20, 2013 at 4:31 PM, carlisle thacker
>> <carlisle.thacker at gmail.com> wrote:
>>> I was looking for something like shown on the map:
>>> http://upload.wikimedia.org/wikipedia/commons/8/88/World_Time_Zones_Map.png
>>>
>>> Information about local daylight savings times would also help.
>>>
>>> The data are from ships, supposedly in local time, but no time- 
>>> zone info is
>>> given.  A function that would return time zone and whether or not  
>>> daylight
>>> savings time applies at given date would would help.  I'm trying  
>>> to track
>>> down more information about the data and whether they can be  
>>> referenced to
>>> UTC.
>>
>> The zone.tab file has this information.  See the Examples section at
>> the end of ?Sys.timezone for info on its whereabouts.
>
> On some OSes only.

This is a couple of snippets of that file from a Mac:
/usr/share/zoneinfo/zone.tab
#-------------
# This file contains a table with the following columns:
# 1.  ISO 3166 2-character country code.  See the file `iso3166.tab'.
# 2.  Latitude and longitude of the zone's principal location
#     in ISO 6709 sign-degrees-minutes-seconds format,
#     either +-DDMM+-DDDMM or +-DDMMSS+-DDDMMSS,
#     first latitude (+ is north), then longitude (+ is east).
# 3.  Zone name used in value of TZ environment variable.
# 4.  Comments; present if and only if the country has multiple rows.
#---------

US	+340308-1181434	America/Los_Angeles	Pacific Time
US	+611305-1495401	America/Anchorage	Alaska Time
US	+581807-1342511	America/Juneau	Alaska Time - Alaska panhandle
US	+593249-1394338	America/Yakutat	Alaska Time - Alaska panhandle neck
US	+643004-1652423	America/Nome	Alaska Time - west Alaska
US	+515248-1763929	America/Adak	Aleutian Islands
US	+211825-1575130	Pacific/Honolulu	Hawaii
UY	-3453-05611	America/Montevideo
UZ	+3940+06648	Asia/Samarkand	west Uzbekistan
UZ	+4120+06918	Asia/Tashkent	east Uzbekistan
VA	+415408+0122711	Europe/Vatican


After looking at it I'm not sure it will be of much additional value  
for the purposes outlined. It does not provide boundaries of time zones.

-- 

David Winsemius, MD
Alameda, CA, USA