Point-in-Polygon Test (1)

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Point-in-Polygon Test (1)
Quasi-C language
... number0 for (i0 iltn i) calculate the
intersection if (Y lt Y0) number If
(int(number/2)20.1lt number) inside the
polygon else outside the polygon ...
(X0, Y0)
(X, Y)
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Point-in-Polygon Test (2)
(Xmax, Ymax)
(X0, Y0)
(Xmin, Ymin)
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Point-in-Polygon Test (3)
(Xi1, Yi1)
(x0, y0)
(Xi, Yi)
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Point-in-Polygon Test (4)
P3
P2
P1
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Hachuring in a Polygon (1)
Y
d
?
o
X
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Hachuring in a Polygon (2)
Y'
Y
Y' Y'max
d
o
X'
-?
Y' Y'min
X
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Douglas-Peucker Algorithm
d (Ax0By0C) / (A2B2)1/2
First anchor point
First floating point
d lt epsilon ?
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Questions for Review (1)

• What is the process of point-in-polygon test
  using vector data? How can we accelerate this
  test?
• How can we avoid troublesome special problems
  when a plumb line in the point-in-polygon test
  passes through the endpoints of two successive
  polygon edges or a perpendicular stretch of
  polygon edge?

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Questions for Review (2)

• Can you give another method of hachuring within a
  polygon which is different from the way we have
  introduced in our class?
• Please describe the global routine of
  Douglas-Peucker algorithm for compressing the
  data of a string.
• Why is the algorithm of Douglas-Peucker widely
  used in digital cartography?