README.md

WhereTZ: timezone lookup

WhereTZ is elixir version of Ruby gem for lookup of timezone by georgraphic coordinates.

https://github.com/zverok/wheretz

Features:

• no calls to external services, works without Internet connection;
• Timezone result is %Timex.TimezoneInfo

Usage

Add to project from hex.pm

def deps do
  [
    {:wheretz, "~> 0.1.17"},
  ]
end

or from github

def deps do
  [
    {:wheretz, git: "[email protected]:UA3MQJ/wheretz.git", tag: "v0.1.17"},
  ]
end

Before the first start, you need to download the geo and initializse the database.

mix where_tz.init 

usage

iex(1)> WhereTZ.get(50.004444, 36.231389)   
#<TimezoneInfo(Europe/Kiev - EET (+02:00:00))>
iex(2)> WhereTZ.lookup(50.004444, 36.231389)
"Europe/Kiev"

How it works

1. Latest version of timezone-boundary-builder dataset is converted into mnesia table (125Mb);
2. For each time zone, store timezone name, geo polygon and calculate bounding box (min and max latitude and longitude);
3. On each lookup WhereTZ first checks provided coordinates by bounding boxes, and if only one bbox, corresponds to them, returns timezone name immediately;
4. If there's several intersecting bounding boxes, WhereTZ checks which polygon actually contains the point.

Known problems

• ?

Author

Alexey Bolshakov

Thanks to

Victor Shepelev

License

Data license is ODbL.

Code license is usual MIT.