当前课程知识点:计算几何 > 04. Voronoi Diagram > F. DCEL > 04-F-01. Twin Edges
好 现在我们就来学习
所谓的DCEL结构
DCEL结构呢
是一种基于边的非常基本的
也是非常通用的一种结构
我们这里介绍的
只是它的最核心的部分
根据不同的应用
你在此后
可以对它做很多的拓展
这是后话
我们接下来看最基本的方法
在这里头最最基本的一种技术
就是所谓的边分解的技术
也就是说我们要将
subdivision中
连接于以任何两个顶点中之间的
那样一条无向的边拆解成两条
或者叫一对有向边
这一对有向边是彼此共存的
互为表里
所以我们也称之为孪生的边
叫做twin edges
这样的一个做法
我们待会就会体会到它的好处
这就犹如一个国家
或者一个城市的交通系统
我们知道
如果你对交通不做任何的约定管理的话
那么路上会非常的乱套的
实际上现代的大部分国家和城市
所采用的方法都是
将同一条路分为
正向和逆向两个方向
比如说在大部分国家都规定
向靠右行驶
但也有一些国家
比如规定向左行驶
具体向左向右没有关系
只要你约定一个就可以
而在这里我们待会看到
也会做一个约定
总而言之
首先这个拆分的技术是最重要的
每一条边会被拆分成
一对称为twin edges的
半边half edges
那么在这个基础上呢
我们还要准备三个记录
或者说有三张表
其中最最基本的那张表
就是edge list边表
它记录的就是
我们刚才这里所拆分出来的
这一系列的半边
现在我们就来逐一的看看
这三类记录分别是如何组成的
它们对应的几何意义又是如何
-Before we start
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-Evaluation
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-Online Judge
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-Lecture notes
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-Discussion
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-A. History of This Course
--00-A. History of This Course
-B. What's Computational Geometry
--00-B. What's Computational Geometry
-B. What's Computational Geometry--作业
-C. How to Learn CG Better
--00-C. How to Learn CG Better
-C. How to Learn CG Better--作业
-D. Why English
-A. Convexity
-A. Convexity--作业
-B. Extreme Points
-B. Extreme Points--作业
-C. Extreme Edges
-C. Extreme Edges--作业
-D. Incremental Construction
--01-D-01. Decrease and Conquer
--01-D-02. In-Convex-Polygon Test
--01-D-03. Why Not Binary Search
-D. Incremental Construction--作业
-E. Jarvis March
--01-E-06. Lowest-Then-Leftmost
-E. Jarvis March--作业
-F. Lower Bound
--01-F-02. CAO Chong's Methodology
-F. Lower Bound--作业
-G. Graham Scan: Algorithm
-G. Graham Scan: Algorithm--作业
-H. Graham Scan: Example
-H. Graham Scan: Example--作业
-I. Graham Scan: Correctness
-I. Graham Scan: Correctness--作业
-J. Graham Scan: Analysis
-J. Graham Scan: Analysis--作业
-K. Divide-And-Conquer (1)
-K. Divide-And-Conquer (1)--作业
-L. Divide-And-Conquer (2)
--01-L-03. Topmost + Bottommost ?
--01-L-07. More Considerations
-L. Divide-And-Conquer (2)--作业
-M. Wrap-Up
-0. Introduction
-0. Introduction--作业
-A. Preliminary
-A. Preliminary--作业
-B. Interval Intersection Detection
-B. Interval Intersection Detection--作业
-C. Segment Intersection Reporting
-C. Segment Intersection Reporting--作业
-D. BO Algorithm: Strategy
--02-D-01. Proximity & Separability
--02-D-02. Comparability & Ordering
-D. BO Algorithm: Strategy--作业
-E. BO Algorithm: Implementation
--02-E-03. Events & Operations
-E. BO Algorithm: Implementation--作业
-F. BO Algorithm: Analysis
--02-F-04. Complexity of Event Queue
--02-F-05. Complexity of Status Structure
-F. BO Algorithm: Analysis--作业
-G. Convex Polygon Intersection Detection
--02-G-01. Problem Specification
--02-G-02. Monotone Partitioning
--02-G-04. Decrease-And-Conquer
-G. Convex Polygon Intersection Detection--作业
-H. Edge Chasing
--02-H-01. Eliminating Sickles
-H. Edge Chasing--作业
-I. Plane Sweeping
-I. Plane Sweeping--作业
-J. Halfplane Intersection Construction
-J. Halfplane Intersection Construction--作业
-0. Methodology
-0. Methodology--作业
-A. Art Gallery Problem
--03-A-02. Lower & Upper Bounds
--03-A-04. Approximation & Classification
-A. Art Gallery Problem--作业
-B. Art Gallery Theorem
--03-B-01. Necessity of floor(n/3)
--03-B-02. Sufficiency by Fan Decomposition
-B. Art Gallery Theorem--作业
-C. Fisk's Proof
--03-C-04. Pigeon-Hole Principle
-C. Fisk's Proof--作业
-D. Orthogonal Polygons
--03-D-01. Necessity of floor(n/4)
--03-D-02. Sufficiency by Convex Quadrilateralization
-D. Orthogonal Polygons--作业
-E. Triangulation
-E. Triangulation--作业
-F. Triangulating Monotone Polygons
--03-F-02. Monotonicity Testing
--03-F-04. Stack-Chain Consistency
-F. Triangulating Monotone Polygons--作业
-G. Monotone Decomposition
-G. Monotone Decomposition--作业
-I. Tetrahedralization
--03-I-01. Polyhedron Decomposition
--03-I-02. Schonhardt's Polyhedron
-I. Tetrahedralization--作业
-A. Introduction
--04-A-02. Dining Halls on Campus
--04-A-03. More Analogies & Applications
-A. Introduction--作业
-B. Terminologies
--04-B-02. Intersecting Halfspaces
--04-B-04. Planar Voronoi Diagram
-B. Terminologies--作业
-C. Properties
--04-C-03. Nearest = Concyclic
--04-C-04. Number of Nearest Sites = Degree
-C. Properties--作业
-D. Complexity
-D. Complexity--作业
-E. Representation
-E. Representation--作业
-F. DCEL
-F. DCEL--作业
-G. Hardness
--04-G-03. Voronoi Diagram In General Position
-G. Hardness--作业
-H. Sorted Sets
--04-H-01. Convex Hull Made Easier
--04-H-02. Convex Hull As A Combinatorial Structure
--04-H-03. Voronoi Diagram As A Geometric Structure
-H. Sorted Sets--作业
-I. VD_sorted
--04-I-06. Sorting Not Made Easier
-I. VD_sorted--作业
-J. Naive Construction
-J. Naive Construction--作业
-K. Incremental Construction
-K. Incremental Construction--作业
-L. Divide-And-Conquer
--04-L-09. Intersecting with Cells
-L. Divide-And-Conquer--作业
-M. Plane-Sweep
--04-M-09. Circle Event: What, When & Where
-M. Plane-Sweep--作业
-A. Point Set Triangulation
-A. Point Set Triangulation--作业
-B. Delaunay Triangulation
-B. Delaunay Triangulation--作业
-C. Properties
-C. Properties--作业
-D. Proximity Graph
--05-D-02. Relative Neighborhood Graph
-D. Proximity Graph--作业
-E. Euclidean Minimum Spanning Tree
-E. Euclidean Minimum Spanning Tree--作业
-F. Euclidean Traveling Salesman Problem
-G. Minimum Weighted Triangulation
-G. Minimum Weighted Triangulation--作业
-H. Construction
--05-H-03. Maximizing The Minimum Angle
--05-H-04. Evolution By Edge Flipping
-H. Construction--作业
-I. RIC With Example
-I. RIC With Example--作业
-J. Randomized Incremental Construction
--05-J-01. Recursive Implementation
--05-J-02. Iterative Implementation
-J. Randomized Incremental Construction--作业
-K. RIC Analysis
--05-K-04. Types Of Edge Change
--05-K-05. Number Of Edge Changes
--05-K-07. Number Of Rebucketings
--05-K-08. Probability For Rebucketing
--05-K-10. Further Consideration
-0. Online/Offline Algorithms
--06-0. Online/Offline Algorithms
-0. Online/Offline Algorithms--作业
-A. Introduction
--06-A-03. Assumptions For Clarity
--06-A-05. Performance Measurements
-A. Introduction--作业
-B. Slab Method
--06-B-02. Ordering Trapezoids
-B. Slab Method--作业
-C. Persistence
--06-C-01. Ephemeral Structure
--06-C-02. Persistent Structure
-C. Persistence--作业
-D. Path Copying
--06-D-03. Storage Optimization
-D. Path Copying--作业
-E. Node Copying
-E. Node Copying--作业
-F. Limited Node Copying
-G. Kirkpatrick Structure
--06-G-01. Optimal And Simpler
--06-G-06. The More The Better
--06-G-07. The Fewer The Better
--06-G-09. Existence Of Independent Subset
--06-G-10. Construction Of Independent Subset
-G. Kirkpatrick Structure--作业
-H. Trapezoidal Map
--06-H-03. Properties & Complexity
--06-H-04. Search Structure: Example
--06-H-05. Search Structure: Nodes
--06-H-06. Search Structure: Performance
-H. Trapezoidal Map--作业
-I. Constructing Trapezoidal Map
--06-I-04. Case 1: Two Endpoints
--06-I-05. Case 2: One Endpoint
--06-I-06. Case 3: No Endpoints
-J. Performance Of Trapezoidal Map
--06-J-03. Number Of Ray Trimmed
--06-J-04. Number Of Trapezoidals Created (1)
--06-J-05. Number Of Trapezoidals Created (2)
--06-J-06. Time For Point Location
--06-J-07. Size Of Search Structure
--06-J-08. Fixed Query Point + Randomly Created Maps
--06-J-10. Probability Of Enclosing Trapezoid Changed
-A. Range Query
--07-A-01. 1-Dimensional Range Query
-A. Range Query--作业
-B. BBST
--07-B-02. Lowest Common Ancestor
-B. BBST--作业
-C. kd-Tree: Structure
-C. kd-Tree: Structure--作业
-D. kd-Tree: Algorithm
-D. kd-Tree: Algorithm--作业
-E. kd-Tree: Performance
--07-E-01. Preprocessing Time + Storage
-E. kd-Tree: Performance--作业
-F. Range Tree: Structure
--07-F-03. x-Query * y-Queries
-F. Range Tree: Structure--作业
-G. Range Tree: Query
-G. Range Tree: Query--作业
-H. Range Tree: Performance
-H. Range Tree: Performance--作业
-I. Range Tree: Optimization
--07-I-04. Fractional Cascading
-A. Orthogonal Windowing Query
-A. Orthogonal Windowing Query--作业
-B. Stabbing Query
-C. Interval Tree: Construction
-C. Interval Tree: Construction--作业
-D. Interval Tree: Query
-D. Interval Tree: Query--作业
-E. Stabbing With A Segment
--08-E-03. Query Algorithm (1)
--08-E-04. Query Algorithm (2)
-F. Grounded Range Query
--08-F-03. 1D-GRQ Using Range Tree
--08-F-04. 1D-GRQ By Linear Scan
-G. 1D-GRQ Using Heap
-G. 1D-GRQ Using Heap--作业
-H. Priority Search Tree
--08-H-03. Sibling Partitioning
-H. Priority Search Tree--作业
-I. 2D-GRQ Using PST
-I. 2D-GRQ Using PST--作业
-J. Segment Tree
--08-J-01. General Windowing Query
--08-J-02. Elementary Interval
--08-J-06. Solving Stabbing Query
--08-J-11. Constructing A Segment Tree
--08-J-12. Inserting A Segment (1)
--08-J-13. Inserting A Segment (2)
--08-J-14. Inserting A Segment (3)
-K. Vertical Segment Stabbing Query