Hi,
I'm having some trouble understanding a few parameters in the TZ database -
everybody knows that.
I'm a developer, in the field of astronomy and celestial mechanics. But I
encountered a problem relative to the relation between Local and UTC time in
one of my applications.
So, I picked up TZ, and tried to analize the cities pm files ( the code must be
adapted, so I need the raw data ).
The long list is compreensible. The problem is the end. For example, for
Europe/Lisbon:
my $last_observance = bless( {
'format' => 'WE%sT',
'gmtoff' => '0:00',
'local_start_datetime' => bless( {
'formatter' => undef,
'local_rd_days' => 728749,
'local_rd_secs' => 7200,
'offset_modifier' => 0,
'rd_nanosecs' => 0,
'tz' => bless( {
'name' => 'floating',
'offset' => 0
}, 'DateTime::TimeZone::Floating' ),
'utc_rd_days' => 728749,
'utc_rd_secs' => 7200,
'utc_year' => 1997
}, 'DateTime' ),
'offset_from_std' => 0,
'offset_from_utc' => 0,
'until' => [],
'utc_start_datetime' => bless( {
'formatter' => undef,
'local_rd_days' => 728749,
'local_rd_secs' => 3600,
'offset_modifier' => 0,
'rd_nanosecs' => 0,
'tz' => bless( {
'name' => 'floating',
'offset' => 0
}, 'DateTime::TimeZone::Floating' ),
'utc_rd_days' => 728749,
'utc_rd_secs' => 3600,
'utc_year' => 1997
}, 'DateTime' )
}, 'DateTime::TimeZone::OlsonDB::Observance' )
;
sub _last_observance { $last_observance }
my $rules = [
bless( {
'at' => '1:00u',
'from' => '1996',
'in' => 'Oct',
'letter' => '',
'name' => 'EU',
'offset_from_std' => 0,
'on' => 'lastSun',
'save' => '0',
'to' => 'max',
'type' => undef
}, 'DateTime::TimeZone::OlsonDB::Rule' ),
bless( {
'at' => '1:00u',
'from' => '1981',
'in' => 'Mar',
'letter' => 'S',
'name' => 'EU',
'offset_from_std' => 3600,
'on' => 'lastSun',
'save' => '1:00',
'to' => 'max',
'type' => undef
}, 'DateTime::TimeZone::OlsonDB::Rule' )
]
;
The rules, are almost readable: for instance DST will start ( even if there's
noreference to "start" ) in the last Sunday of March of any year equal or
greater than 1981. But, at what time? The rule is:
Continental Portugal > UTC+1 from the last Sunday in March at 01:00 to
the last Sunday in October at 02:00 Europe/Lisbon
How do we figure this from the above ? - that I don't understand ( I must be
blind or tired... ); and other situations with other values occurr with
different countries.
Can someone explain me the calculations regarding every fields to get to the
rule FROM THE PM CITY FILE ( this is important ! )? I would appreciate it very
much - and it would save most of my time.
Kind regards,
Rui Miguel Fernandes
Porto - Portugal
