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eastar

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Eastar is a pure-Elixir implementation of A* graph pathfinding algorithm. All graph environment, like nodes connectivity, distance & H-metric are abstracted away - you provide them as functions.

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eastar lib utils hgeo.ex
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lib/utils/hgeo.ex 

defmodule Astar.Utils.H.Geo do

  @moduledoc """

  Exposes H-function as a shortest distance between

  two points on Earth globe, plus a number of conversion

  functions.

  """



  import :math



  @pi_by_180    pi/180

  @earth_radius 6371





  def to_deg({deg, min, sec}), do:

    deg + min/60 + sec/3600

  def to_deg(a) when is_number(a), do: a



  def to_radian(a), do:

    (a |> to_deg) * @pi_by_180





  def h({lat1, lon1}, {lat2, lon2}) do

    phi1 = lat1 |> to_radian

    phi2 = lat2 |> to_radian

    dphi = ((lat2 |> to_deg) - (lat1 |> to_deg)) |> to_radian

    dl   = ((lon2 |> to_deg) - (lon1 |> to_deg)) |> to_radian



    sp = sin(dphi/2)

    sl = sin(dl/2)

    a = sp*sp + cos(phi1)*cos(phi2)*sl*sl

    c = 2*atan2(sqrt(a), sqrt(1-a))

    @earth_radius * c

  end

end