Solving Voronoi Diagram Problems: Coordinates, Bisectors, and Restaurant Choices

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Understanding Perpendicular Bisectors in Voronoi Diagrams

  • A perpendicular bisector is a line perpendicular to a segment that passes through its midpoint.
  • Given points A and B, with B at coordinates (4,6), the perpendicular bisector line L is given by the equation y = -2x + 9.
  • The slope of line L is -2, so the slope of segment AB is the opposite reciprocal, 1/2.

Finding the Equation of Line AB

  • Using point B (4,6) and slope 1/2, the equation of line AB is derived using point-slope form:
    • y - 6 = 1/2(x - 4)

Finding the Intersection Point M (Midpoint of AB)

  • M lies on both line AB and the perpendicular bisector L.
  • Solve the system:
    • y - 6 = 1/2(x - 4)
    • y = -2x + 9
  • Solving yields M at (2,5).

Calculating Coordinates of Point A

  • M is the midpoint of segment AB, so:
    • M_x = (x_A + 4)/2 = 2 → x_A = 0
    • M_y = (y_A + 6)/2 = 5 → y_A = 4
  • Therefore, A is at (0,4).

Determining Closest Restaurant Using Voronoi Cells

  • Elena at (27,27) is closest to restaurant B because her location lies within B's Voronoi cell.
  • If restaurant A is closed, the closest restaurant to a point in A's cell is the next nearest, e.g., restaurant F.
  • Voronoi cells guarantee any point inside is closer to its associated site than any other.

Perpendicular Bisector of Segment CD

  • Restaurants C and D are at (7,8) and (7,5) respectively.
  • Midpoint of CD is (7,6.5).
  • Since CD is vertical, the perpendicular bisector is horizontal: y = 6.5.

Finding Perpendicular Bisector of Segment BC

  • B at (3,6), C at (7,8).
  • Midpoint of BC: ((3+7)/2, (6+8)/2) = (5,7).
  • Slope of BC: (8-6)/(7-3) = 2/4 = 1/2.
  • Slope of perpendicular bisector: opposite reciprocal of 1/2 is -2.
  • Equation of perpendicular bisector passing through midpoint:
    • y - 7 = -2(x - 5)

Finding Point P Equidistant from B, C, and D

  • P lies at the intersection of the perpendicular bisectors of BC and CD.
  • Solve system:
    • y = 6.5
    • y - 7 = -2(x - 5)
  • Substituting y = 6.5 into second equation gives x = 5.25.
  • So, P is at (5.25, 6.5).

Calculating Distance from P to D

  • D is at (7,5).
  • Distance formula:
    • d = √[(5.25 - 7)^2 + (6.5 - 5)^2] ≈ 2.30 km.

Criticism of Using Voronoi Cell Area to Predict Restaurant Popularity

  • Larger Voronoi cell area does not necessarily mean more customers.
  • Factors like population density and accessibility affect customer numbers.
  • Area alone is insufficient to predict restaurant popularity.

This summary provides step-by-step methods to solve coordinate geometry problems related to Voronoi diagrams, including finding midpoints, slopes, perpendicular bisectors, and interpreting Voronoi cells for practical applications like choosing the closest restaurant.

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