Module: Measurable::Haversine

Included in:
Measurable
Defined in:
lib/measurable/haversine.rb

Instance Method Summary collapse

Instance Method Details

#haversine(u, v, unit = :meters) ⇒ Object

call-seq:

haversine(u, v) -> Float

Compute accurate distances between two points given their latitudes and longitudes, even for short distances. This isn’t a distance measure in the same sense as the other methods in Measurable.

The distance returned is the great circle (or orthodromic) distance between u and v, which is the shortest distance between them on the surface of a sphere. Thus, this implementation considers the Earth to be a sphere.

Reminding that the input vectors are of the form [latitude, longitude] in degrees, so if you have the coordinates [23 32’ S, 46 37’ W] (from São Paulo), the corresponding vector is [-23.53333, -46.61667].

References:

Arguments:

  • u -> An array of Numeric objects.

  • v -> An array of Numeric objects.

  • unit -> (Optional) A Symbol representing the unit of measure. Available

    options are +:miles+, +:feet+, +:km+ and +:meters+.

Returns:

  • The great circle distance between u and v.

Raises:

  • ArgumentError -> The size of u and v must be 2.

  • ArgumentError -> unit must be a Symbol.

Raises:

  • (ArgumentError) 


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# File 'lib/measurable/haversine.rb', line 50

def haversine(u, v, unit = :meters)
  # TODO: Create better exceptions.
  raise ArgumentError if u.size != 2 || v.size != 2
  raise ArgumentError if unit.class != Symbol

  dlat = u[0] - v[0]
  dlon = u[1] - v[1]

  dlon_rad = dlon * RAD_PER_DEG
  dlat_rad = dlat * RAD_PER_DEG

  lat1_rad = v[0] * RAD_PER_DEG
  lon1_rad = v[1] * RAD_PER_DEG

  lat2_rad = u[0] * RAD_PER_DEG
  lon2_rad = u[1] * RAD_PER_DEG

  a = (Math.sin(dlat_rad / 2)) ** 2 + Math.cos(lat1_rad) * Math.cos(lat2_rad) * (Math.sin(dlon_rad / 2)) ** 2
  c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a))

  EARTH_RADIUS[unit] * c
end