Class: SimplifyRb

Inherits:
Object
  • Object
show all
Defined in:
lib/simplify_rb.rb,
lib/simplify_rb/version.rb

Constant Summary collapse

VERSION = 
"0.1.2"

Class Method Summary collapse

Class Method Details

.getSqDist(point_1, point_2) ⇒ Object

Square distance between two points



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# File 'lib/simplify_rb.rb', line 69

def self.getSqDist (point_1, point_2)
  dx = point_1[:x] - point_2[:x]
  dy = point_1[:y] - point_2[:y]

  dx * dx + dy * dy
end

.getSqSegDist(point, point_1, point_2) ⇒ Object

Square distance from a point to a segment



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# File 'lib/simplify_rb.rb', line 77

def self.getSqSegDist (point, point_1, point_2)
  x  = point_1[:x]
  y  = point_1[:y]
  dx = point_2[:x] - x
  dy = point_2[:y] - y

  if (dx != 0 || dy != 0)
    t = ((point[:x] - x) * dx + (point[:y] - y) * dy) / (dx * dx + dy * dy)

    if t > 1
      x = point_2[:x]
      y = point_2[:y]

    elsif t > 0
      x += dx * t
      y += dy * t
    end
  end

  dx = point[:x] - x
  dy = point[:y] - y

  dx * dx + dy * dy
end

.keys_are_symbols?(keys) ⇒ Boolean

Check if keys are symbols

Returns:

  • (Boolean) 


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# File 'lib/simplify_rb.rb', line 103

def self.keys_are_symbols? (keys)
  keys.all? {|k| k.is_a? Symbol}
end

.simplify(points, tolerance = 1, highest_quality = false) ⇒ Object

Main method

Raises:

  • (ArgumentError) 


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# File 'lib/simplify_rb.rb', line 5

def self.simplify (points, tolerance=1, highest_quality=false)
  raise ArgumentError.new('Points must be an array') unless points.is_a? Array

  return points if points.length <= 1

  points = symbolize_keys(points) unless keys_are_symbols?(points.map(&:keys))

  sq_tolerance = tolerance * tolerance

  # Optimisation step 1
  points = simplifyRadialDist(points, sq_tolerance) unless highest_quality

  # Optimisation step 2
  simplifyDouglasPeucker(points, sq_tolerance)
end

.simplifyDouglasPeucker(points, sq_tolerance) ⇒ Object

Simplification using optimized Douglas-Peucker algorithm with recursion elimination



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# File 'lib/simplify_rb.rb', line 35

def self.simplifyDouglasPeucker (points, sq_tolerance)
  first = 0
  last  = points.length - 1
  index = nil
  stack = []

  points.first[:keep] = true
  points.last[:keep]  = true

  while last do
    max_sq_dist = 0

    ((first + 1)...last).each do |i|
      sq_dist = getSqSegDist(points[i], points[first], points[last])

      if sq_dist > max_sq_dist
        index = i
        max_sq_dist = sq_dist
      end
    end

    if max_sq_dist > sq_tolerance
      points[index][:keep] = true

      stack.push(first, index, index, last)
    end

    first, last = stack.pop(2)
  end # end while

  points.select { |p| p[:keep] && p.delete(:keep) }
end

.simplifyRadialDist(points, sq_tolerance) ⇒ Object

Basic distance-based simplification



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# File 'lib/simplify_rb.rb', line 22

def self.simplifyRadialDist (points, sq_tolerance)
  new_points = [points.first]

  points.each do |point|
    new_points << point if (getSqDist(point, new_points.last) > sq_tolerance)
  end

  new_points << points.last unless new_points.last == points.last

  new_points
end

.symbolize_keys(collection) ⇒ Object

Symbolize all the hash keys in an array of hashes



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# File 'lib/simplify_rb.rb', line 108

def self.symbolize_keys (collection)
  collection.map do |item|
    item.each_with_object({}) { |(k,v), memo| memo[k.to_sym] = v }
  end
end