[tz] Beginner's help request

[Brian Inglis]

On 2017-10-16 12:42, Matt Johnson wrote:
> On Saturday, October 14, 2017 5:45 AM, Daniel Ford wrote:
>> I'm looking to develop a 'world clock' that could be sold to anyone (with
>> Internet access via a Wi-Fi AP) anywhere in the world, that will display
>> their local time, taking into account DST if/when applicable.
>> Given that DST 'rules' can change at the whim of governments, my firmware
>> will need to annually look up 'current' DST rules from the web.  After much
>> searching, it seems that your TZ Database is the best supported such
>> reference for time zone rules.  But I'm having great difficulty working out
>> how I might access its mine of information...
>> (I'll understand if you don't have time to help out a beginner, and maybe
>> then you could refer me to a help site for TZ database applications.)
>> I'm a hardware engineer with some programming experience, particularly
>> assembler (various MCUs) and some C, but little or no experience in other
>> languages.  I'm developing this clock on an Arduino-like platform (NodeMCU,
>> which has in-built Wi-Fi).  My development tools run on a Win7Pro64 PC.
>> The tools that you kindly provide for your database appear to be geared
>> primarily towards Linux/Unix platforms, and I have no idea how I might
>> convert them for a NodeMCU!  I'm looking for some 'simple' way to access the
>> desired TZ/DST information, preferably using simple string searches.
>> For my application, all I'm interested in are the *current* rules.  The
>> wealth of history in your db is undoubtedly of interest to many, but for me
>> is just 'clutter' to be searched through.  But writing a program to find
>> those rules for a particular locality has me stumped right now.  I can't
>> expect my dumb users to know a letter code for their time-zone/DST-rules, so
>> all I'm expecting them to select from program-generated lists are: (1) their
>> world region (Europe, Asia, Australasia, etc), and (2) the name of a major
>> city in their time-zone with the same DST rules they follow.
>> Let's take a concrete example: say my user has nominated 'Australasia' and
>> 'Hobart'.  So I look in your Australasia file and do a (manual at this
>> stage) search for 'Hobart', but find only one reference to it (other than in
>> comments).  The jumble of numbers and letters there do not (clearly) tell me
>> when DTS starts or ends.  So how could I possibly write some code to find
>> out that required information??
>> I've looked through the TZ_database-2017b.tar file for some sort of 'how-to'
>> explanation of what all the file contents mean and how to programmatically
>> search for a specific TZ, but have so far found nothing.
>> Ideally, what I'd like to see is a text-only table of just current TZ/DST
>> rules for each region/locality (they could all fit into a single file with
>> all the historical data and comments removed), perhaps in the clear form
>> used by Jack Christensen in his excellent Arduino Timezone library examples,
>> such as...
>> // Australia Eastern Time Zone (Sydney, Melbourne, Hobart)
>> TimeChangeRule aEDT = {"AEDT", First, Sun, Oct, 2, 660};
>> TimeChangeRule aEST = {"AEST", First, Sun, Apr, 3, 600};
>> TimezoneExt ausET("NSW, Vic, Tas", aEDT, aEST);
>> // Australia Eastern Time Zone (Brisbane)
>> TimezoneExt QldT("Queensland", aEST, aEST);  // no DST in Qld!
>> ... which clearly tells me in a program-searchable way that in the main
>> eastern states DST starts on the first Sunday in October at 2am, becoming
>> UTC offset +11 hours (660 minutes), and ends on the first Sunday in April at
>> 3am, reverting to UTC offset +10 hours.  Couldn't be simpler!
>> Any help in using the TZ database will be much appreciated (and acknowledged
>> in my source code).

> One thing to keep in mind - the TZ database is prolific, and already has 
> widespread adoption in many platforms, languages and libraries. Sure, there
> are many cases where one might need to go back to the sources, but most of
> the time there's already work of others to leverage.> In the case of the NodeMCU platform, I suggest you start with the "TZ" LUA
> module, shown here:> https://github.com/nodemcu/nodemcu-firmware/tree/master/lua_examples/timezone
> You'll want to use current data files though, rather than the few that are
> given there. You should be able to generate them with the zic compiler from
> this project (though getting it working on Windows is tricky) - or you can
> just gather them precompiled from any tzdata distribution on a Linux system.
Also available by installing Cygwin and/or Ubuntu for Windows, which include
tzdata in their base installs, and using Windows File Explorer to search for the
zoneinfo directory.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada