Class: SimplifyRb

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

Constant Summary collapse

VERSION = 
"0.1.3"

Class Method Summary collapse

Class Method Details

.get_sq_dist(point_1, point_2) ⇒ Object

Square distance between two points



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# File 'lib/simplify_rb.rb', line 72

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

  dx * dx + dy * dy
end

.get_sq_seg_dist(point, point_1, point_2) ⇒ Object

Square distance from a point to a segment



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# File 'lib/simplify_rb.rb', line 80

def self.get_sq_seg_dist(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

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

Raises:

  • (ArgumentError) 


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# File 'lib/simplify_rb.rb', line 6

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

  symbolizer = SimplifyRbUtils::Symbolizer.new

  points = symbolizer.symbolize_keys(points) unless points.all? { |p| symbolizer.keys_are_symbols?(p.keys) }

  sq_tolerance = tolerance * tolerance

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

  # Optimisation step 2
  simplify_douglas_peucker(points, sq_tolerance)
end

.simplify_douglas_peucker(points, sq_tolerance) ⇒ Object

Simplification using optimized Douglas-Peucker algorithm with recursion elimination



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# File 'lib/simplify_rb.rb', line 38

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

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

  while last
    max_sq_dist = 0

    ((first + 1)...last).each do |i|
      sq_dist = get_sq_seg_dist(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

.simplify_radial_dist(points, sq_tolerance) ⇒ Object

Basic distance-based simplification



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# File 'lib/simplify_rb.rb', line 25

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

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

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

  new_points
end