[tz] Beginner's help request

Daniel Ford dfnojunk at gmail.com
Sun Oct 15 04:40:22 UTC 2017


Thanks for your comments, which I'll address before the other feedback I've received, since the others will require more considered responses...

Firmware planning has barely started, but my current intention is to have the NodeMCU start-up (first-time only) in Wi-Fi AP mode, with a specified SSID/password.  So the user will be expected to log onto that AP to work through the set-up pages.

Apart from the user's own SSID/Password (for their own 'home' AP), no free-form text will be allowed.  They must select first their 'region', from a displayed list, and then their 'reference city' from another displayed list (which, of course, will only contain cities from the *nominated* region).  So naturally I'll choose those region and city names to be compatible with those used in the TZdb.



From: Sanjeev Gupta [mailto:ghane0 at gmail.com] 
Sent: Sunday, October 15, 2017 3:24 PM
To: Daniel Ford
Cc: tz at iana.org
Subject: Re: [tz] Beginner's help request

> 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).

If you allow the user to enter the City Name, please note that the user might enter "Hovarta", which is the (made-up) localised version of the name of the city.  cf Kolkotta, Wien, etc

This issue turns up regularly on the list (along with "But that is not the biggest city, including suburbs).  The TZ database does not deal with UI issues, in this respect, you will have to handle them.

Will your clock have a UI?  Accessible as a web page, or with up/down/select buttons?

Sanjeev Gupta
+65 98551208     http://www.linkedin.com/in/ghane

On Sat, Oct 14, 2017 at 8:45 PM, Daniel Ford <dfnojunk at gmail.com> 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).
	Daniel Ford (Gerroa, Australia)
	"My loathings are simple: stupidity, oppression, crime, cruelty, soft
	music." - Vladimir Nabokov

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