Class: Geospatial::Hilbert::Curve

Inherits:
Object
  • Object
show all
Defined in:
lib/geospatial/hilbert/curve.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(dimensions, order = 30) ⇒ Curve 



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# File 'lib/geospatial/hilbert/curve.rb', line 27

def initialize(dimensions, order = 30)
  raise ArgumentError("Order #{order} must be positive integer!") unless order >= 1
  
  # Order is the number of levels of the curve, which is equivalent to the number of bits per dimension.
  @order = order
  @scale = 2**@order
  
  @dimensions = dimensions * @scale
  @origin = dimensions.origin
  @size = dimensions.size
end

Instance Attribute Details

#dimensions ⇒ Object (readonly)

Returns the value of attribute dimensions.



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# File 'lib/geospatial/hilbert/curve.rb', line 41

def dimensions
  @dimensions
end

#order ⇒ Object (readonly)

Returns the value of attribute order.



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# File 'lib/geospatial/hilbert/curve.rb', line 39

def order
  @order
end

#scale ⇒ Object (readonly)

Returns the value of attribute scale.



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# File 'lib/geospatial/hilbert/curve.rb', line 40

def scale
  @scale
end

Instance Method Details

#bit_width ⇒ Object 



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# File 'lib/geospatial/hilbert/curve.rb', line 62

def bit_width
  @dimensions.count
end

#map(coordinates) ⇒ Object 



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# File 'lib/geospatial/hilbert/curve.rb', line 92

def map(coordinates)
  axes = @dimensions.map(coordinates).map(&:floor)
  
  index = OrdinalIndex.new(axes, @order)
  
  return index.to_hilbert.to_i
end

#origin ⇒ Object 



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# File 'lib/geospatial/hilbert/curve.rb', line 43

def origin
  @dimensions.origin
end

#size ⇒ Object 



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# File 'lib/geospatial/hilbert/curve.rb', line 47

def size
  @dimensions.size
end

#to_s ⇒ Object 



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# File 'lib/geospatial/hilbert/curve.rb', line 51

def to_s
  "\#<#{self.class} order=#{@order} dimensions=#{@dimensions}>"
end

#traverse(&block) ⇒ Object

This is a helper entry point for traversing Hilbert space.



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# File 'lib/geospatial/hilbert/curve.rb', line 56

def traverse(&block)
  return to_enum(:traverse) unless block_given?
  
  traverse_recurse(@order-1, 0, 0, self.origin, self.size, &block)
end

#traverse_recurse(order, mask, value, origin, size, &block) ⇒ Object

Traversal enumerates all regions of a curve, top-down.



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# File 'lib/geospatial/hilbert/curve.rb', line 67

def traverse_recurse(order, mask, value, origin, size, &block)
  half_size = size.collect{|value| value * 0.5}.freeze
  prefix_mask = (1 << order) | mask
  
  (2**bit_width).times do |prefix|
    # These both do the same thing, not sure which one is faster:
    child_value = (value << @dimensions.count) | prefix
    prefix = child_value << (order*bit_width)
    
    index = HilbertIndex.from_integral(prefix, bit_width, @order).to_ordinal
    
    index = index & prefix_mask
    
    child_origin = @dimensions.unmap(index.axes).freeze
    
    # puts "yield(#{child_origin}, #{half_size}, #{prefix}, #{order})"
    # We avoid calling traverse_recurse simply to hit the callback on the leaf nodes:
    result = yield child_origin, half_size, prefix, order
    
    if order > 0 and result != :skip
      self.traverse_recurse(order - 1, prefix_mask, child_value, child_origin, half_size, &block)
    end
  end
end

#unmap(value) ⇒ Object 



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# File 'lib/geospatial/hilbert/curve.rb', line 100

def unmap(value)
  index = HilbertIndex.from_integral(value, @dimensions.count, @order)
  
  return @dimensions.unmap(index.to_ordinal.axes)
end