Class: Ballistics::Projectile

Inherits:
Object
  • Object
show all
Defined in:
lib/ballistics/projectile.rb

Constant Summary collapse

YAML_DIR = 
'projectiles'
MANDATORY = 
{
  "name"   => :string,
  "cal"    => :float,
  "grains" => :count,
}
BALLISTIC_COEFFICIENT =

one of these fields is mandatory

{
  "g1" => :float,
  "g7" => :float,
}
OPTIONAL = 
{
  "sd"       => :float,
  "intended" => :string,
  "base"     => :string,
  "desc"     => :string,
}
DRAG_FUNCTION = 
{
  "flat" => "g1",
  "boat" => "g7",
}
DRAG_NUMBER = 
{
  "g1" => 1,
  "g7" => 7,
}

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(hsh) ⇒ Projectile

Returns a new instance of Projectile.



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# File 'lib/ballistics/projectile.rb', line 63

def initialize(hsh)
  @yaml_data = hsh
  MANDATORY.each { |field, type|
    val = hsh.fetch(field)
    Ballistics::YAML.check_type!(val, type)
    self.instance_variable_set("@#{field}", val)
  }

  # Extract ballistic coefficients per drag model (e.g. G1)
  # We need at least one
  #
  @ballistic_coefficient = {}
  BALLISTIC_COEFFICIENT.each { |field, type|
    if hsh.key?(field)
      val = hsh[field]
      if !Ballistics::YAML.check_type?(val, type)
        raise(TypeError, "#{val} (#{field}) is not #{type}")
      end
      self.instance_variable_set("@#{field}", val)
      @ballistic_coefficient[field] = val
    end
  }
  raise "no valid BC" if @ballistic_coefficient.empty?

  OPTIONAL.each { |field, type|
    if hsh.key?(field)
      val = hsh[field]
      val = val.to_s if field == "intended" and type == :string
      Ballistics::YAML.check_type!(val, type)
      if field == "base"
        @base = self.class.base(val)
      else
        self.instance_variable_set("@#{field}", val)
      end
    end
  }

  # Keep track of fields that we don't expect
  @extra = {}
  (hsh.keys -
   MANDATORY.keys -
   BALLISTIC_COEFFICIENT.keys -
   OPTIONAL.keys).each { |k|
    @extra[k] = hsh[k]
  }

  # Make sure @base and @drag_function are initialized so that
  # self.drag_function works without warnings
  #
  @base ||= nil
  @drag_function = nil
end

Instance Attribute Details

#ballistic_coefficient ⇒ Object (readonly)

Returns the value of attribute ballistic_coefficient.



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# File 'lib/ballistics/projectile.rb', line 61

def ballistic_coefficient
  @ballistic_coefficient
end

#extra ⇒ Object (readonly)

Returns the value of attribute extra.



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# File 'lib/ballistics/projectile.rb', line 61

def extra
  @extra
end

#yaml_data ⇒ Object (readonly)

Returns the value of attribute yaml_data.



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# File 'lib/ballistics/projectile.rb', line 61

def yaml_data
  @yaml_data
end

Class Method Details

.base(candidate) ⇒ Object

Normalize common flat-base and boat-tail terms to flat or boat



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# File 'lib/ballistics/projectile.rb', line 40

def self.base(candidate)
  c = candidate.to_s.downcase.gsub(/[\-\_ ]/, '')
  case c
  when "boat", "boattail", "bt"
    "boat"
  when "flat", "flatbase", "fb"
    "flat"
  else
    raise "unknown base: #{candidate}"
  end
end

.drag_number(drag_function) ⇒ Object

Convert e.g. G1 to 1



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# File 'lib/ballistics/projectile.rb', line 54

def self.drag_number(drag_function)
  DRAG_NUMBER.fetch(drag_function.to_s.downcase)
end

.find(file: nil, id: nil) ⇒ Object

Load a built-in YAML file and instantiate projectile objects Return a hash of projectile objects keyed by projectile id (per the YAML)



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# File 'lib/ballistics/projectile.rb', line 34

def self.find(file: nil, id: nil)
  Ballistics::YAML.find(klass: self, file: file, id: id)
end

Instance Method Details

#bc ⇒ Object

Return the BC for the preferred drag function



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# File 'lib/ballistics/projectile.rb', line 132

def bc
  @ballistic_coefficient.fetch(self.drag_function)
end

#drag_function ⇒ Object

Return the preferred drag function if there is a BC available



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# File 'lib/ballistics/projectile.rb', line 118

def drag_function
  return @drag_function if @drag_function
  @drag_function = @ballistic_coefficient.keys.first
  if @base
    preferred = DRAG_FUNCTION.fetch(@base)
    if @ballistic_coefficient.key?(preferred)
      @drag_function = preferred
    end
  end
  @drag_function
end

#multiline ⇒ Object

Return lines of text separated by newlines



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# File 'lib/ballistics/projectile.rb', line 146

def multiline
  lines = ["PROJECTILE: #{@name}", "=========="]
  fields = {
    "Caliber" => @cal,
    "Grains" => @grains,
  }
  @ballistic_coefficient.each { |df, bc|
    fields["BC (#{df.upcase})"] = bc
  }
  fields["Desc"] = @desc if @desc
  fields.each { |name, val|
    lines << [name.rjust(7, ' '), val].join(': ')
  }
  lines.join("\n")
end

#params ⇒ Object

Return params that can be used by Ballistics::Problem



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# File 'lib/ballistics/projectile.rb', line 138

def params
  { drag_function: self.drag_function,
    drag_number: self.class.drag_number(self.drag_function),
    ballistic_coefficient: self.bc }
end