From: ara.t.howard@...
Date: 2006-08-09T06:20:15+09:00
Subject: Re: solar local time

On Wed, 9 Aug 2006, Tim Pease wrote:

> ZONES = class << Time; ZoneOffset.keys.map {|x| x.length == 1 ? x :
> nil}.compact.sort; end
> ZONES.unshift ZONES.pop
>
> def move_to_zone( utc, longitude )
> zone = ZONES[Integer(longitude) / Integer(DEG_PER_HR)]
> utc - Time.zone_offset(zone)
> end
>
> This does not take into account daylight savings, etc.  But give it a
> shot and see if it's what you need.

it's close, but check this out:

     harp:~ > cat a.rb
     require 'time'

     class Time
       ZONES =
         class << self
           (_ = ZoneOffset.keys.select{|z| z.size == 1}.sort).unshift(_.pop)
         end
       def translated longitude
         zone = ZONES[Integer(longitude) / 15]
         utc - Time.zone_offset(zone)
       end
     end

     t = Time.parse('1999-12-31T23:59:59Z') or 'party like it is'

     require 'yaml'

     [0, 15, 16, 30, 31].each do |degrees|
       y degrees => t.translated(degrees).iso8601

       y -degrees => t.translated(-degrees).iso8601
     end


     harp:~ > ruby a.rb
     0: "1999-12-31T23:59:59Z"
     0: "1999-12-31T23:59:59Z"
     15: "1999-12-31T22:59:59Z"
     -15: "2000-01-01T11:59:59Z"
     16: "1999-12-31T22:59:59Z"
     -16: "2000-01-01T10:59:59Z"
     30: "1999-12-31T21:59:59Z"
     -30: "2000-01-01T10:59:59Z"
     31: "1999-12-31T21:59:59Z"
     -31: "2000-01-01T09:59:59Z"


take one example

     15: "1999-12-31T22:59:59Z"

the time is correct but the zone is not.  consider, 15 degrees to the east of 0
longitude at '1999-12-31T23:59:59Z' the solar local time is

     '1999-12-31T22:59:59+01:00'

make sense?

-a
-- 
to foster inner awareness, introspection, and reasoning is more efficient than
meditation and prayer.
- h.h. the 14th dali lama