Time Zones via GPS anyone know?

mctrivia · 2010-05-14 12:48

I am trying to figure out how to find the current time zone when I know the longitude and latitude but can't find any kind of map or code snipet to do this. anyone know how?

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PJAllen · 2010-05-14 12:57

Time zones correspond only roughly·to the meridians.· Zones stray from meridians in almost every, if not every,·instance.· If you can find a position and have an extensive database to·reference then you could determine your time zone.

http://24timezones.com/

Post Edit -- The whole of Red China is on Peking time.

Post Edited (PJ Allen) : 5/14/2010 1:02:12 PM GMT

mctrivia · 2010-05-14 13:10

Yes I know. I am trying to get that extensive database. but though I can find pictures of where the time zone boarders are. I can't seem to find a polygon map that I can compare my point to.

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Unknown · 2010-05-14 13:11

I entered this into google as:

how do you find the time zone for a gps?

And the first link on the list provided some clues.

http://www.vbrad.com/article.aspx?id=35

mctrivia · 2010-05-14 13:17

that sounds like what I want. But I do not see an option to download the code and the code shown does not show how to do it.

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PJAllen · 2010-05-14 13:34

That'll be an extensive database even with a coarse granularity.

0 N, 0E = __; 0N, 1E = __;...

mctrivia · 2010-05-14 13:44

It would have to be in the form of regions not pixels.

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Unknown · 2010-05-14 14:27

I think the key to solving this is knowing how you dould do this in your head by using a paper map, pencil, paper, calculator, etc before you take it to a computer or microcontroller.

"Standard time zones can be defined by geometrically subdividing the Earth's spheroid into 24 lunes (wedge-shaped sections), bordered by meridians each 15° of longitude apart. The local time in neighboring zones would differ by one hour. However, political boundaries, geographical practicalities, and convenience of inhabitants can result in irregularly-shaped zones. Moreover, in a few regions, half-hour or quarter-hour differences are in effect."

http://en.wikipedia.org/wiki/Time_zone

mctrivia · 2010-05-14 14:41

in canada if I was looking at a map i would determine which province the location was in first as most time zones align themselves with provincial boarders.

With a calculator/computer it is relitively easy to compute if a location is within a triangular region. If we made a map of the world out of triangles I would first search for all triangles anywear near my location then compute if I am within any of them

for example the following code generates a search query of my picture database to see if there are any pictures close to the designated location. It is quick and dirty but it reduces the large database down to a small number of results which I can then do more accurate calculations on.

function SQLclosepictures($lat,$long,$d) {
  $latmax = $lat+($d/111.222222);
  $latmin = $lat-($d/111.222222);
  if ((abs($latmax)>90) or (abs($latmin)>90)) {
    return 'SELECT * FROM `pics` WHERE `latitude`>' . $latmin . ' AND `latitude`<' . $latmax;
  } else {
    $l=abs($long);
    if ($l<5) {
      $ls = $d/111.2;
    } elseif ($l<10) {
      $ls = $d/110.8;
    } elseif ($l<15) {
      $ls = $d/109.5;
    } elseif ($l<20) {
      $ls = $d/107.4;
    } elseif ($l<25) {
      $ls = $d/104.5;
    } elseif ($l<30) {
      $ls = $d/100.8;
    } elseif ($l<35) {
      $ls = $d/96.3;
    } elseif ($l<40) {
      $ls = $d/91.09;
    } elseif ($l<45) {
      $ls = $d/85.18;
    } elseif ($l<50) {
      $ls = $d/78.63;
    } elseif ($l<55) {
      $ls = $d/71.47;
    } elseif ($l<60) {
      $ls = $d/63.78;
    } elseif ($l<65) {
      $ls = $d/55.6;
    } elseif ($l<70) {
      $ls = $d/46.99;
    } elseif ($l<75) {
      $ls = $d/38.03;
    } elseif ($l<80) {
      $ls = $d/28.78;
    } else {
      $ls = $d/19.31;
    }
    $longmax = $long+$ls;
    $longmin = $long-$ls;
    return 'SELECT * FROM `pics` WHERE `latitude`>' . $latmin . ' AND `latitude`<' . $latmax . ' AND `longitude`>' . $longmin . ' AND `longitude`<' . $longmax;
  }
}

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Phil Pilgrim (PhiPi) · 2010-05-14 17:06

geonames.org probably has the info you need in their downloadable database, but it doesn't look like it's in a very convenient form for what you're trying to do. Their forum (forum.geonames.org/gforum/forums/list.page) may have people more knowledgeable about the subject, who could help you more than we can.

-Phil

mctrivia · 2010-05-14 18:09

Thanks. It does not look like they store time zone info but I have asked anyways to see. Since my application is for a web server I can always have it poll another web site to do the conversion for me but it would be nice to find the information so I can also right an object for the propeller(though I am sure an SD card would be needed)

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mctrivia · 2010-05-14 18:21

found an internet solution

http://worldtimeengine.com/dotime/n49.837405_w99.934820/

where n49.837405_w99.934820 is the location. should not be to hard to parse and gives all needed info.

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Phil Pilgrim (PhiPi) · 2010-05-14 20:41

'Didn't realize your app was net-connected. Here's a short tutorial on doing it in Ruby with geonames.org: chrischandler.name/ruby/converting-latitude-and-longitude-to-timezones/.

-Phil

mctrivia · 2010-05-14 20:47

well parsing the xml returned from http://ws.geonames.org/timezone?lat=49.837405&lng=-99.934820 will be a lot easier then the site i mentioned. the site is coded in php so I can't use there function but it will be easy to write my own based off it. thanks.

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Cluso99 · 2010-05-16 10:18

Next you will have to consider Daylight Saving and the fact that it keeps varying, well at least in Australia it does!

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CannibalRobotics · 2013-02-01 11:38

I don't think zip codes cross time zones as they are driven by the same political boarders. Here is a zip code database with all of the time zones.
http://www.zipinfo.com/products/z5p/z5p.htm I'll bet there is also a listing of lat/lon for establishing zip by GPS.

Prophead100 · 2013-02-01 18:19

Take a look at the "Solar" object on the OBEX. The method "Merdian_Calc" will determine the closest meridian then its a simple divide by 15 degree to get the hour offset for the local time zone. The code will also show you some examples of floating point math.

Mark_T · 2013-02-03 05:37

Just a random thought - how far offshore do timezones extend? In mid-ocean clearly one can default to the 15 degree segments, but near land presumably the
local coastline's timezone would apply? This page seems to answer these questions and mentions the tricky problem of working out maps of territorial v. internation waters:
http://efele.net/maps/tz/world/

Heater. · 2013-02-03 06:38

mctrivia,

That timezone service is very nice, they have lots of other good stuff there as well. The response will be even easier to parse if you ask for JSON format.

Request:

http://ws.geonames.org/timezoneJSON?lat=49.837405&lng=-99.934820

Respnse:

{"time":"2013-02-03 08:31",
"countryName":"Canada",
"sunset":"2013-02-03 17:37",
"rawOffset":-6,
"dstOffset":-5,
"countryCode":"CA",
"gmtOffset":-6,
"lng":-99 .93482,
"sunrise":"2013-02-03 08:10",
"timezoneId":"America/Winnipeg",
"lat":49.837405
}

LoopyByteloose · 2013-02-03 08:24

I happen to reside in the world's largest time zone since China prefers to have one and only one for their entire nation and I coincidently align with the zone it is supposed to be.

Over 1 billion 344 million people have just one time zone! Odd, very odd.

But it seems no one has mentioned the other bugaboo, Daylight Savings Time. And of course, there is double daylight savings, war time, and other adjustments that overlay time zones.

I presume the goal is to determine what time the person at a given location thinks it should be.

Please note the offset in the above listing -- raw offsett, dst offset, and gmt offset.

Time Zones via GPS anyone know?

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