Re: pw_images, UTC, TimeZones, LocalTime

[Phil P. <phi...@sw...>]

Here are some of my random thoughts on enabling sunrise/sunset 
calculations in PHP Weather.

Current entries in pw_stations = 5130
Entries from NOAA (http://weather.noaa.gov/data/nsd_cccc.txt) = 6486

- Read the NOAA datafile and update pw_stations
	- additional fields for LAT and LONG, STATE, ALTITUDE
	- add records for new STATIONS (1356 new entries)

Goal: finding current 'offset from UTC including Daylight Savings if 
required' for a station

Source: the Public Domain TimeZone Database
(http://www.twinsun.com/tz/tz-link.htm)

As well as being a database of all the timezones
	including their DST usage
	zone.tab lists (amongst other things)
		ISO 3166 2-character country code
		TimeZone used
			
So, we can match a CC from our stations list to an entry from zone.tab
(for speed put the TimeZone into a field in pw_stations)

This tells us which timezone to use.
In theory, getting the total offset from GMT should then be as simple as
	$realTZ = getenv('TZ');
	putenv ("TZ=$timeZone");
	$GMT_offset = date('O');
	putenv("TZ=$realTZ");
				
.... Now we have
	ICAO
	Name
	ISO CC
	Country Name
	State
	Latitude
	Longitude
	current GMT offset including DST
	
Grab PHP example code from http://www.zend.com/codex.php?id=135&single=1

I ran a check with co-ords for Sydney, given a hard-coded $DST=1
	this code produces data correct to within 10 minutes
	ie good enough for our uses
	
- tweak code
- not calculate DST , just needs $GMT_offset_including_DST
- accept co-ordinates as either DMS or decimal
	(ie auto-convert DMS to decimal)
- input params
	( GMT DATE,  lat, long , local GMT offset including DST )
- returns list($sunriseTimeStamp, $sunsetTimeStamp)
	
- hack code in pw_images.php
	to identify night_or_day via these calculations

Thoughts/comments/suggestions?

Phil P

Phil Pierotti wrote:
> A little trolling around on the web found me THIS interesting chunk of 
> PHP code:
> 
> http://www.zend.com/codex.php?id=135&single=1
> 
> Specificallly, an implementation of calculating sunrise and set from 
> LAT+LONG+GMT Offset
> 
> Enjoy,
> Phil P
> 
> 
> Martin Geisler wrote:
> 
>> Phil Pierotti <phi...@sw...> writes:
>>
>>
>>> Realistically, for this to be complete and flexible, each ICAO will
>>> need the following information:
>>>     - TimeZone specified as offset from GMT
>>>     - uses Daylight Savings?
>>>     - DST start date
>>>     - DST end date
>>>     - latitude & longitude
>>>
>>> The sunrise and sunset times can be calculated from the information
>>> from NOAA http://www.srrb.noaa.gov/highlights/sunrise/calcdetails.html
>>
>>
>>
>> Thanks a lot for that link --- we've made an attempt to implement this
>> kind of functionality before, but when I searched the net I only found
>> some messy algorithms that I didn't have much luck with, see
>>
>>   http://makeashorterlink.com/?T162215A2
>>
>> The information on the above page looks much clearer, and it should be
>> easy to port the JavaScript code to PHP --- those two languages are
>> very much alike.
>>
>>
>>> Lat and Long can be had for ICAOs from
>>> http://weather.noaa.gov/tg/site.shtml directly ->
>>> http://weather.noaa.gov/data/nsd_cccc.txt
>>
>>
>>
>> Thanks again --- I've found those datafiles before, but the
>> information is still not part of PHP Weather.  Given the latitude and
>> longitude it should be possible to calculate an approximate timezone.
>>
>> And with that timezone we should be able to give a local time for the
>> reports, but I guess it will still be off by +/- 1 hours depending on
>> daylight saving time, so I don't know how good that idea is.
>>
>> It's just that the real solution: attaching detailed information about
>> the daylight saving time to each station, sounds like a difficult
>> task.  But then again, there must be some tables with this information
>> somewhere on every system, so perhaps it's doable?
>>
>>
>> In any case --- I'm having my exams right now!  The first one will be
>> on Wednesday, so I wont start playing with this stuff now, but if
>> someone else feels like it, then by all mean do!  I can add people to
>> the project as developers if they believe they need CVS access.
>>
> 
> 
> 
> -------------------------------------------------------
> The SF.Net email is sponsored by EclipseCon 2004
> Premiere Conference on Open Tools Development and Integration
> See the breadth of Eclipse activity. February 3-5 in Anaheim, CA.
> http://www.eclipsecon.org/osdn
> _______________________________________________
> PHPWeather-devel mailing list
> PHP...@li...
> https://lists.sourceforge.net/lists/listinfo/phpweather-devel
> 
>