Class: Geospatial::Peaks

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
lib/geospatial/histogram.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(values) ⇒ Peaks

Returns a new instance of Peaks.



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# File 'lib/geospatial/histogram.rb', line 110

def initialize(values)
  @values = values
  @derivative = []
  
  s = @values.size
  
  @values.size.times do |i|
    # Apply the Laplacian of Gaussians to compute the gradient changes:
    # @derivative << (@values[i-2] * -1) + (@values[i-1] * -1) + (@values[i] * 4) + (@values[i+1-s] * -1) + (@values[i+2-s] * -1)
    @derivative << (2.0 * @values[i-1]) + (-2.0 * @values[i+1-s])
  end
end

Instance Attribute Details

#derivative ⇒ Object (readonly)

Returns the value of attribute derivative.



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# File 'lib/geospatial/histogram.rb', line 123

def derivative
  @derivative
end

Instance Method Details

#each ⇒ Object 



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# File 'lib/geospatial/histogram.rb', line 125

def each
  return to_enum unless block_given?
  
  @derivative.each_with_index do |y2, x2|
    x1 = x2 - 1
    y1 = @derivative[x1]
    
    if (y1 <= 0 and y2 > 0) or (y1 > 0 and y2 <= 0)
      # There has been a zero crossing, so we have a peak somewhere here:
      g = (y2.to_f - y1.to_f)
      m = (-y1.to_f / g)
      
      yield x1 + m, g
    end
  end
end

#peaks ⇒ Object 



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# File 'lib/geospatial/histogram.rb', line 142

def peaks
  self.class.new(@derivative)
end

#segments ⇒ Object 



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# File 'lib/geospatial/histogram.rb', line 146

def segments
  return to_enum(:segments) unless block_given?
  
  peaks = self.peaks
  gradients = peaks.to_a
  
  return if gradients.empty?
  
  index, gradient = gradients.first
  
  if gradient > 0
    gradients.push gradients.shift
  end
  
  gradients.each_slice(2) do |up, down|
    yield up, down
  end
end