Ruby Gem For Finding Timezone of Location

Ruby gem for finding timezone of location

You can easily get a latitude and longitude using the google maps geocoding API. There are ruby implementations for the API like GeoKit. Once you have that you can use the timezone gem to easily get the timezone of a latitude and longitude. The gem makes it easy to do time conversions in your timezone as well.

Here is an example using GeoKit and TimeZone.

require 'geokit'
require 'timezone'

res = Geokit::Geocoders::GoogleGeocoder.geocode('140 Market St, San Francisco, CA')
timezone = Timezone::Zone.new(:latlon => res.ll)

timezone.zone
=> "America/Los_Angeles"
timezone.time Time.now
=> 2011-12-01 14:02:13 UTC

get timezone from location name in Ruby on Rails

You could download the geonames db and compare lat/lng to the nearest place (with timezone) in the db

Download the database of cities from geonames.org
convert it to a compact lat/lon -> timezone list

How to get Timezone with geocode gem?

You cannot get timezone directly from geocoder gem.
It can just give you location.

You can use the gem below to get the timezone for a particular zone or for (lat,long) values.

https://github.com/panthomakos/timezone

timezone = Timezone::Zone.new :latlon => [-34.92771808058, 138.477041423321]
timezone.zone
=> "Australia/Adelaide"
timezone.time Time.now
=> 2011-02-12 12:02:13 UTC

How do I get the utc offset from an address?

Geolocate the address to lat/lon coordinates using any number of web services for this. Then see the options in How to get a time zone from a location using latitude and longitude coordinates? The Ruby gem that Yevgeniy mentioned is listed there, along with other options.

Don't try to get an offset for the location - it could change periodically for DST. Get the time zone instead, such as Asia/Singapore or America/New_York. Then use that to determine the offset for a particular point in time.

See "Time Zone != Offset" in the timezone tag wiki.

Linking datetimes of events to their associated location timezone (TimeZone gem, ActiveSupport::TimeWithZone)

User enters a datetime (year, month, day, hour, min, sec) in the appropriate local time for the event location. To save this as the correct UTC time in your DB, and retrieve later retrieve it and use it with its correct timezone, here's the recipe:

You must first set Time.zone = timezone -- where timezone is a named timezone string, like "America/Toronto" (GeoKit/TimeZone style) or "Eastern Time (US & Canada)" (Rails 3 style):
```
1.9.3p200 :001 > Time.zone = "America/Toronto"
 => "America/Toronto"
```
Note that it is nontrivial to map between the GeoKit/TimeZone style and the Rails 3 style. There is some support for that, but many of the mappings that GeoKit returns are not in the Rails mappings, so I'm sticking with the GeoKit/TimeZone names because they seem to work just fine, and I don't need user-selectable timezones because I'm taking care of all of that automagically for the user using the locations.
Now you can parse and save your datetime variable using ActiveSupport::TimeWithZone, and it will be encoded properly using the Time.zone parameter:
```
1.9.3p200 :002 > t = Time.zone.local( 2012, 8, 1, 12, 0, 0 )
 => Wed, 01 Aug 2012 12:00:00 EDT -04:00 
```
i.e. In my case, for my Event model with instance event:
```
event.start = Time.zone.local( year, month, day, hour, min, sec )
event.save
```
When the data is saved to the DB, it is in UTC: 2012-08-01 16:00:00.000000
(Simulated below with call to t.utc)
```
1.9.3p200 :003 > t = t.utc
 => 2012-08-01 16:00:00 UTC

1.9.3p200 :004 > t.zone
 => "UTC" 
```

Now, when you read it back from the DB, you need to again use the TimeWithZone support to tell the DateTime what timezone it is in.

Note that the in_time_zone function does not change the underlying datetime variable's timezone:

1.9.3p200 :005 > t.in_time_zone( "America/Toronto" )
 => Wed, 01 Aug 2012 12:00:00 EDT -04:00 

1.9.3p200 :006 > t
 => 2012-08-01 16:00:00 UTC 

1.9.3p200 :007 > t.zone
 => "UTC"

so you really need to assign the function output back to your datetime variable:

1.9.3p200 :008 > t = t.in_time_zone( "America/Toronto" )
 => Wed, 01 Aug 2012 12:00:00 EDT -04:00 

1.9.3p200 :009 > t
 => Wed, 01 Aug 2012 12:00:00 EDT -04:00 

1.9.3p200 :010 > t.zone
 => "EDT"

Finally, a warning -- do not use t.time! It's output is completely useless and irrational, with the time and it's timezone out of sync:
```
1.9.3p200 :011 > t.time
 => 2012-08-01 12:00:00 UTC 
```

Getting timezone in pure Ruby (no rails)

For the time being, this works TZ=Asia/Kolkata ruby -e "p Time.new(1942).strftime('%z')"

Setting the TZ environment variable also works from within Ruby: (seen in test_time_tz.rb)

def with_tz(tz)
  old = ENV['TZ']
  ENV['TZ'] = tz
  yield
ensure
  ENV['TZ'] = old
end

with_tz('Asia/Kolkata') do
  (1935..1945).each do |x|
    puts "#{x} => #{Time.local(x).strftime('%z')}"
  end
end

How to get a time zone from a location using latitude and longitude coordinates?

Time Zone Location Web Services

Google Maps Time Zone API
Bing Maps Time Zone API
Azure Maps Time Zone API
GeoNames Time Zone API
TimeZoneDB API
AskGeo - commercial (but arguably more accurate than GeoNames)
GeoGarage Time Zone API - commercial, focusing on Nautical time zones.

Raw Time Zone Boundary Data

Timezone Boundary Builder - builds time zone shapefiles from OpenStreetMaps map data. Includes territorial waters near coastlines.

The following projects have previously been sources of time zone boundary data, but are no longer actively maintained.

tz_world - the original shapefile data from Eric Muller
whereonearth-timezone - GeoJSON version with WOEDB data merged in

Time Zone Geolocation Offline Implementations

Implementations that use the Timezone Boundary Builder data

node-geo-tz - JavaScript library (Node.js only)
timespace - JavaScript library
tz-lookup-oss - JavaScript library
GeoTimeZone - .NET library
Geo-Timezone - PHP library
timezonefinder - Python library
ZoneDetect - C library
Timeshape - Java library
TimeZoneMap - Java and Android library
lutz - R library
go-tz - Go library
Timezone lookup - Go library
docker-timezone-lookup - docker container wrapping node-geo-tz

Implementations that use the older tz_world data

latlong - Go library (Read this post also.)
TimeZoneMapper - Java library
tzwhere - JavaScript/Node library
pytzwhere - Python library
timezone_finder - Ruby library
LatLongToTimeZone - Java and Swift libraries
What Time is it here? - Blog post describing PHP and MongoDB
rundel/timezone - R library

Libraries that call one of the web services

timezone - Ruby gem that calls GeoNames
AskGeo has its own libraries for calling from Java or .Net
GeoNames has client libraries for just about everything

Self-hosted web services

geo2tz - based on Timezone lookup, available via Docker image

Other Ideas

Find the nearest city with an R-Tree
Find the nearest city with MySQL

Please update this list if you know of any others

Also, note that the nearest-city approach may not yield the "correct" result, just an approximation.

Conversion To Windows Zones

Most of the methods listed will return an IANA time zone id. If you need to convert to a Windows time zone for use with the TimeZoneInfo class in .NET, use the TimeZoneConverter library.

Don't use zone.tab

The tz database includes a file called zone.tab. This file is primarily used to present a list of time zones for a user to pick from. It includes the latitude and longitude coordinates for the point of reference for each time zone. This allows a map to be created highlighting these points. For example, see the interactive map shown on the moment-timezone home page.

While it may be tempting to use this data to resolve the time zone from a latitude and longitude coordinates, consider that these are points - not boundaries. The best one could do would be to determine the closest point, which in many cases will not be the correct point.

Consider the following example:

Time Zone Example Art

The two squares represent different time zones, where the black dot in each square is the reference location, such as what can be found in zone.tab. The blue dot represents the location we are attempting to find a time zone for. Clearly, this location is within the orange zone on the left, but if we just look at closest distance to the reference point, it will resolve to the greenish zone on the right.

Ruby Gem For Finding Timezone of Location