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 172

def compute_speed
  awa = @awa.abs
  if awa < 0.75
    @speed = 0.0
    return
  end
  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

#compute_wind ⇒ Object

Compute the wind (as a Bearing) based on the compass heading and the apparent wind as reported.



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# File 'lib/sgs/course.rb', line 165

def compute_wind
  @wind.angle = @heading + @awa
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. If you’re computing angles to one waypoint, the relative VMG will allow you to compare against each possible angle. If you’re computing to different waypoints, then the distance from your position to that waypoint is taken into consideration so that waypoints further away have less impact on your VMG choice.



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# File 'lib/sgs/course.rb', line 158

def relative_vmg(waypt)
  @speed * Math::cos(waypt.bearing.angle - @heading) / waypt.distance
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 192

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