class Geospatial::Hilbert::Curve

Attributes

dimensions[R]
order[R]
scale[R]

Public Class Methods

new(dimensions, order = 30) click to toggle source
# 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

Public Instance Methods

bit_width() click to toggle source
# File lib/geospatial/hilbert/curve.rb, line 62
def bit_width
        @dimensions.count
end
map(coordinates) click to toggle source
# 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() click to toggle source
# File lib/geospatial/hilbert/curve.rb, line 43
def origin
        @dimensions.origin
end
size() click to toggle source
# File lib/geospatial/hilbert/curve.rb, line 47
def size
        @dimensions.size
end
to_s() click to toggle source
# File lib/geospatial/hilbert/curve.rb, line 51
def to_s
        "\#<#{self.class} order=#{@order} dimensions=#{@dimensions}>"
end
traverse(&block) click to toggle source

This is a helper entry point for traversing Hilbert space.

# 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) { |child_origin, half_size, prefix, order| ... } click to toggle source

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

# 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) click to toggle source
# 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