Class: GpxDoctor::PointSelector

Inherits:
Object
  • Object
show all
Defined in:
lib/gpx_doctor/point_selector.rb

Instance Method Summary collapse

Instance Method Details

#select(points, max_points) ⇒ Object

Selects up to max_points points from points with equal distance spread. Always includes the first and last points. Returns a new array; the original is not mutated. When points already has fewer or equal elements than max_points, it is returned unchanged.



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# File 'lib/gpx_doctor/point_selector.rb', line 18

def select(points, max_points)
  return points if points.nil? || max_points <= 0 || points.size <= max_points

  m = points.size
  n = max_points

  # For n == 1 there is no denominator (n - 1 = 0), so just keep the first point.
  return [points[0]] if n == 1

  cumulative = [0.0]
  points.each_cons(2) do |a, b|
    cumulative << cumulative.last + DistanceCalculator.distance(a, b)
  end
  total = cumulative.last

  # Degenerate case: all points are at the same location — fall back to index spread.
  if total.zero?
    indices = (0...n).map { |i| (i * (m - 1).to_f / (n - 1)).round }
    return indices.uniq.map { |idx| points[idx] }
  end

  used = {}
  selected_indices = (0...n).map do |i|
    target = i * total / (n - 1).to_f
    # Find the closest unused point to the target cumulative distance.
    best_idx = cumulative
      .each_with_index
      .reject { |_, idx| used[idx] }
      .min_by { |d, _| (d - target).abs }
      .last
    used[best_idx] = true
    best_idx
  end

  selected_indices.sort.map { |idx| points[idx] }
end

#total_distance(points) ⇒ Object

Returns the total distance in meters for a sequence of points.



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# File 'lib/gpx_doctor/point_selector.rb', line 6

def total_distance(points)
  return 0.0 if points.nil? || points.size < 2

  total = 0.0
  points.each_cons(2) { |a, b| total += DistanceCalculator.distance(a, b) }
  total
end