Class: RGeo::Cartesian::Segment

Inherits:
Object
  • Object
show all
Defined in:
lib/rgeo/cartesian/calculations.rb

Overview

Represents a line segment in the plane.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(start, stop) ⇒ Segment

:nodoc:



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# File 'lib/rgeo/cartesian/calculations.rb', line 14

def initialize(start, stop)
  @s = start
  @e = stop
  @sx = @s.x
  @sy = @s.y
  @ex = @e.x
  @ey = @e.y
  @dx = @ex - @sx
  @dy = @ey - @sy
  @lensq = @dx * @dx + @dy * @dy
end

Instance Attribute Details

#dx ⇒ Object (readonly)

Returns the value of attribute dx.



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# File 'lib/rgeo/cartesian/calculations.rb', line 26

def dx
  @dx
end

#dy ⇒ Object (readonly)

Returns the value of attribute dy.



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# File 'lib/rgeo/cartesian/calculations.rb', line 26

def dy
  @dy
end

#e ⇒ Object (readonly)

Returns the value of attribute e.



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# File 'lib/rgeo/cartesian/calculations.rb', line 26

def e
  @e
end

#s ⇒ Object (readonly)

Returns the value of attribute s.



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# File 'lib/rgeo/cartesian/calculations.rb', line 26

def s
  @s
end

Instance Method Details

#contains_point?(point) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/rgeo/cartesian/calculations.rb', line 59

def contains_point?(point)
  if side(point) == 0
    t = tproj(point)
    t && t >= 0.0 && t <= 1.0
  else
    false
  end
end

#degenerate? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/rgeo/cartesian/calculations.rb', line 37

def degenerate?
  @lensq == 0
end

#eql?(other) ⇒ Boolean Also known as: ==

Returns:

  • (Boolean) 


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# File 'lib/rgeo/cartesian/calculations.rb', line 32

def eql?(other)
  other.is_a?(Segment) && @s == other.s && @e == other.e
end

#intersects_segment?(seg) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/rgeo/cartesian/calculations.rb', line 68

def intersects_segment?(seg)
  !segment_intersection(seg).nil?
end

#length ⇒ Object 



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# File 'lib/rgeo/cartesian/calculations.rb', line 141

def length
  Math.sqrt(@lensq)
end

#segment_intersection(seg) ⇒ RGeo::Feature::Point?

If this and the other segment intersect, this method will return the coordinate at which they intersect, otherwise nil. In the case of a partial overlap (parallel segments), this will return a single point on the overlapping portion.

Parameters:

Returns:



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# File 'lib/rgeo/cartesian/calculations.rb', line 80

def segment_intersection(seg)
  s2 = seg.s
  # Handle degenerate cases
  if seg.degenerate?
    return @s if @lensq == 0 && @s == s2

    return contains_point?(s2) ? s2 : nil
  elsif @lensq == 0
    return seg.contains_point?(@s) ? @s : nil
  end

  # Both segments have nonzero length.
  sx2 = s2.x
  sy2 = s2.y
  dx2 = seg.dx
  dy2 = seg.dy
  denom = @dx * dy2 - @dy * dx2

  if denom == 0
    # Segments are parallel. Make sure they are collinear.
    return nil unless side(s2) == 0

    # return the first point it finds that intersects another line.
    # In many cases, the intersection is actually another line
    # segment, but for now, we will just return a single point.
    return s2 if contains_point?(s2)
    return seg.e if contains_point?(seg.e)
    return @s if seg.contains_point?(@s)
    return @e if seg.contains_point?(@e)
    nil
  else
    # Segments are not parallel. Check the intersection of their
    # containing lines.
    num1 = dx2 * (@sy - sy2) - (dy2 * (@sx - sx2))
    num2 = @dx * (@sy - sy2) - (@dy * (@sx - sx2))
    cross1 = num1 / denom
    cross2 = num2 / denom

    return nil if cross1 < 0.0 || cross1 > 1.0
    if cross2 >= 0.0 && cross2 <= 1.0
      x = @sx + (cross1 * @dx)
      y = @sy + (cross1 * @dy)

      # Check if this segment contains the point.
      # Sometimes round-off errors occur and intersections
      # are recorded as off the line segments.
      #
      # If this is the case, return the closest point from
      # either segment.
      int_pt = @s.factory.point(x, y)

      return int_pt if contains_point?(int_pt)

      # find closest of @s, @e, seg.s, seg.e
      [@e, seg.s, seg.e].reduce(@s) do |closest, pt|
        int_pt.distance(pt) < int_pt.distance(closest) ? pt : closest
      end
    end
  end
end

#side(point) ⇒ Object

Returns a negative value if the point is to the left, a positive value if the point is to the right, or 0 if the point is collinear to the segment.



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# File 'lib/rgeo/cartesian/calculations.rb', line 45

def side(point)
  px = point.x
  py = point.y
  (@sx - px) * (@ey - py) - (@sy - py) * (@ex - px)
end

#to_s ⇒ Object 



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# File 'lib/rgeo/cartesian/calculations.rb', line 28

def to_s
  "#{@s} - #{@e}"
end

#tproj(point) ⇒ Object 



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# File 'lib/rgeo/cartesian/calculations.rb', line 51

def tproj(point)
  if @lensq == 0
    nil
  else
    (@dx * (point.x - @sx) + @dy * (point.y - @sy)) / @lensq
  end
end