Module: Cross::Track::Distance

Defined in:
lib/cross/track/distance.rb,
lib/cross/track/distance/version.rb

Constant Summary collapse

VERSION = 
"1.0.0"
@@R =

Earth ratio in meters

6371000

Class Method Summary collapse

Class Method Details

.bearing(from, to) ⇒ Object

www.movable-type.co.uk/scripts/latlong.html



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# File 'lib/cross/track/distance.rb', line 28

def self.bearing(from, to)
  #  see http://mathforum.org/library/drmath/view/55417.html
  # phi_1 = from.lat to radians
  # phi_2 = to.lat to radians
  # delta_lambda = to.lon - from.lon to radians
  # y = sin(d_lambda) * cos(phi_2)
  # x = cos(phi_1) * sin(phi_2) - sin(phi_1)*cos(phi_2) * cos(delta_lambda)
  # thita = atan2(y, x)
  # (thita to_degrees  + 360) % 360)
  phi_1 = from[:lat].to_rad
  phi_2 = to[:lat].to_rad
  delta_lambda= (to[:lon] - from[:lon]).to_rad
  y = Math::sin(delta_lambda) * Math::cos(phi_2)
  x = Math::cos(phi_1) * Math::sin(phi_2) - Math::sin(phi_1) * Math::cos(phi_2) * Math::cos(delta_lambda)
  thita = Math::atan2(y,x)
  #puts from
  #puts to
  #puts phi_1
  #puts phi_2
  #puts delta_lambda
  #puts y
  #puts x
  #puts thita
  (thita.to_deg + 360) % 360
end

.cross_track_distance(segment_start_pt, segment_end_pt, point) ⇒ Object

Calculates the shortest distance from point to the segment line on a great circle. segment_start_pt is point in which the segment starts. It’s a hash with :lat and :lon segment_end_pt is point in which the segment ends. It’s a hash with :lat and :lon point is the point to calculate the distance to the segment.

Returns the distance in meters



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# File 'lib/cross/track/distance.rb', line 61

def self.cross_track_distance(segment_start_pt, segment_end_pt, point)
  #var δ13 = pathStart.distanceTo(this, radius)/radius;
  #var θ13 = pathStart.bearingTo(this).toRadians();
  #var θ12 = pathStart.bearingTo(pathEnd).toRadians();
  #var dxt = Math.asin( Math.sin(δ13) * Math.sin(θ13-θ12) ) * radius;

  #puts segment_start_pt
  #puts segment_end_pt
  #puts point

  delta_13 = Haversine.distance(segment_start_pt[:lat],segment_start_pt[:lon],point[:lat],point[:lon]).to_m / @@R
  thita_13 = Cross::Track::Distance::bearing(segment_start_pt, point).to_rad
  thita_12 = Cross::Track::Distance::bearing(segment_start_pt, segment_end_pt).to_rad

  #puts delta_13
  #puts thita_13
  #puts thita_12

  Math::asin(Math::sin(delta_13) * Math::sin(thita_13 - thita_12) ) * @@R

end