From: "Ara.T.Howard" <ara.t.howard@...>
Date: 2006-08-09T07:42:30+09:00
Subject: Re: solar local time

On Tue, 8 Aug 2006, Tim Pease wrote:

> That does make sense.  Here's what I came up with based on that ...
>
> class Time
>
> OFFSETS = class << self; ZoneOffset end
> ZONES = OFFSETS.keys.select {|z| z.length == 1}.sort
> ZONES.unshift ZONES.pop
>
> def translate longitude
>   zone = ZONES[Integer(longitude) / 15]
>   t = utc - ::Time.zone_offset(zone)
>
>   unless zone == 'Z'
>     zone = OFFSETS[zone]
>     str = t.iso8601
>
>     str.sub! %r/Z$/, ''
>     str << (zone > 0 ? '-' : '+')
>     str << "%02d:00" % zone.abs
>
>     t = Time.iso8601 str
>   end
>
>   return t
> end
> end
>
>
> I had to go through and intermediary string in order to get into the
> right timezone.  Printing out the returned Time object says it is
> still in UTC, but that doesn't matter.  It's in the correct timezone
> for your parsing needs.
>
> If that doesn't work or is not what you want, just shot me a private
> e-mail with your work number and I'll cal you

too funny.  this is a sketch of my code so far:


     off_sec =
       if longitude > 180.0
         ((360.0 - longitude) / DEG_PER_HR) * SECS_PER_HR
       else
         (longitude / DEG_PER_HR) * SECS_PER_HR
       end

     signedness = off_sec > 0 ? +1 : -1
     sign = signedness > 0 ? '+' : '-'

     hour_offset, r = off_sec.to_i.abs.divmod SECS_PER_HR
     min_offset, r = r.divmod SECS_PER_MIN

     hour_offset *= signedness

     zone = '%s%-02.2d:%-02.2d' % [sign, hour_offset.to_i, min_offset.to_i.abs]

     utc_plus_off = time + off_sec

     localtime_expressed_in_utc = Time.parse(utc_plus_off.sub(%r/Z$/, zone)).utc


look familiar ;-)

yeah - this will do it - the time is expressed in utc but at least it's the
actual correct time with respect the ground sampled by the bird at that moment.

thanks for the help - the fact that you came up with that independently makes
me feel better.

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