Class: SGS::Course

Inherits:
Object
  • Object
show all
Defined in:
lib/sgs/course.rb

Overview

A class to handle the course sailed, as well as polar speed calculations. For speed calculations, it takes a range of polars as polynomials and then applies them.

Constant Summary collapse

TACK_NAME = 
["Starboard", "Port"].freeze
STARBOARD = 
0
PORT = 
1
STANDARD =

Right now, we have one polar - from a Catalina 22. Note that the speed is the same, regardless of the tack.

[
   -3.15994,
   23.8741,
  -27.4595,
   16.4868,
   -5.15663,
    0.743936,
   -0.0344716
].freeze

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(wind = nil) ⇒ Course

Set up the default values



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# File 'lib/sgs/course.rb', line 71

def initialize(wind = nil)
  @polar_curve = STANDARD
  @awa = 0.0
  @speed = 0.0
  @wind = wind || Bearing.new(0.0, 10.0)
  @heading = nil
  self.heading = 0
end

Instance Attribute Details

#awa ⇒ Object

Returns the value of attribute awa.



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# File 'lib/sgs/course.rb', line 49

def awa
  @awa
end

#polar_curve=(value) ⇒ Object (writeonly)

Sets the attribute polar_curve

Parameters:

  • value —

    the value to set the attribute polar_curve to.



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# File 'lib/sgs/course.rb', line 50

def polar_curve=(value)
  @polar_curve = value
end

#speed ⇒ Object (readonly)

Returns the value of attribute speed.



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# File 'lib/sgs/course.rb', line 49

def speed
  @speed
end

Instance Method Details

#awa_d ⇒ Object

Return the Apparent Wind Angle (AWA) in degrees



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# File 'lib/sgs/course.rb', line 100

def awa_d
  Bearing.rtod @awa
end

#compute_speed ⇒ Object

Compute the hull speed from the polar. This is just a guestimate of how fast the boat will travel at the particular apparent wind angle.



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# File 'lib/sgs/course.rb', line 162

def compute_speed
  awa = @awa.abs
  return 0.0 if awa < 0.75
  ap = 1.0
  @speed = 0.0
  @polar_curve.each do |poly_val|
    @speed += poly_val * ap
    ap *= awa
  end
  @speed /= 2.5           # Fudge for small boat
  if @speed < 0.0
    @speed = 0.0
  end
end

#heading ⇒ Object

Return the current heading



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# File 'lib/sgs/course.rb', line 82

def heading
  @heading
end

#heading=(new_heading) ⇒ Object

Set the heading



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# File 'lib/sgs/course.rb', line 118

def heading=(new_heading)
  return if @heading and @heading == new_heading
  if new_heading > 2*Math::PI
    new_heading -= 2*Math::PI
  elsif new_heading < 0.0
    new_heading += 2*Math::PI
  end
  @heading = new_heading
  self.awa = @wind.angle - @heading
end

#heading_d ⇒ Object

Return the heading in degrees



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# File 'lib/sgs/course.rb', line 88

def heading_d
  Bearing.rtod @heading
end

#relative_vmg(waypt) ⇒ Object

Compute a relative VMG based on the waypoint



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# File 'lib/sgs/course.rb', line 153

def relative_vmg(waypt)
  relvmg = @speed * Math::cos(waypt.bearing.angle - @heading) / waypt.distance
  puts "Relative VMG to WPT: #{waypt.name} is #{relvmg}"
  relvmg
end

#tack ⇒ Object

Return the current tack



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# File 'lib/sgs/course.rb', line 106

def tack
  (@awa and @awa < 0.0) ? PORT : STARBOARD
end

#tack_name ⇒ Object

Return the tack name



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# File 'lib/sgs/course.rb', line 112

def tack_name
  TACK_NAME[tack]
end

#to_s ⇒ Object

Convert to a string



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# File 'lib/sgs/course.rb', line 179

def to_s
  "Heading %dd (wind %.1f@%dd, AWA:%dd, speed=%.2fknots)" % [heading_d, wind.distance, wind.angle_d, awa_d, speed]
end

#wind ⇒ Object

Return the wind direction/speed



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# File 'lib/sgs/course.rb', line 94

def wind
  @wind
end

#wind=(new_wind) ⇒ Object

Set the wind direction and recompute the AWA if appropriate. Note that we don’t care about wind speed (for now)



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# File 'lib/sgs/course.rb', line 132

def wind=(new_wind)
  return if @wind and @wind.angle == new_wind.angle
  @wind = new_wind
  self.awa = @wind.angle - @heading
end