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

Returns a new instance of 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