ClipperOffset偏移类在GIS中具体应用有哪些详细解释？

第16章：ClipperOffset 偏移类详解 16.1 概述 ClipperOffset 类用于对多边形和路径进行偏移（膨胀或收缩）操作。这在 CAD、CNC 加工、地图缓冲区分析等领域有广泛应用。 16.2 类定义 16.2.1 类声明 public class ClipperOffset { // 选项 private double _miterLimit; private double _arcTolerance; private bool _preserveCollinear; private bool _reverseSolution; // 内部数据 private readonly List<Group> _groupList; private readonly PathD _normals; private readonly Paths64 _solution; // delta 相关 private double _groupDelta; private double _delta; private double _absGroupDelta; private double _mitLimSqr; private double _stepsPerRad; private double _stepSin; private double _stepCos; // 构造函数 public ClipperOffset(double miterLimit = 2.0, double arcTolerance = 0.25, bool preserveCollinear = false, bool reverseSolution = false) { _miterLimit = miterLimit; _arcTolerance = arcTolerance; _preserveCollinear = preserveCollinear; _reverseSolution = reverseSolution; _groupList = new List<Group>(); _normals = new PathD(); _solution = new Paths64(); } } 16.2.2 Group 类 internal class Group { internal Paths64 paths; internal JoinType joinType; internal EndType endType; internal bool pathsReversed; public Group(Paths64 paths, JoinType joinType, EndType endType) { this.paths = paths; this.joinType = joinType; this.endType = endType; } } 16.3 JoinType 连接类型 16.3.1 枚举定义 public enum JoinType { Miter, // 斜接 Square, // 方形 Bevel, // 斜角 Round // 圆角 } 16.3.2 Miter（斜接） 原始： Miter 偏移： ╲ ╱│ ╲ ╱ │ ╲ ╱ │ ╲──────────╱ │ │ │ 延伸两条偏移边到相交点 受 MiterLimit 限制 16.3.3 Square（方形） 原始： Square 偏移： ╲ ┌─┐ ╲ ╱ │ ╲ ╱ │ ╲──────────╱─────┘ 在拐角处添加方形 16.3.4 Bevel（斜角） 原始： Bevel 偏移： ╲ ╱ ╲ ╱│ ╲ ╱ │ ╲──────────╱───┘ 直接连接两条偏移边 16.3.5 Round（圆角） 原始： Round 偏移： ╲ ╭─╮ ╲ ╱ ╲ ╲ ╱ │ ╲──────────╱──────╯ 使用圆弧连接 16.4 EndType 端点类型 16.4.1 枚举定义 public enum EndType { Polygon, // 闭合多边形 Joined, // 连接的开放路径 Butt, // 平头 Square, // 方形端 Round // 圆形端 } 16.4.2 各类型图示 原始路径：○────────────────○ Polygon (闭合): ┌──────────────────┐ │ │ │ ○────────────○ │ │ │ └──────────────────┘ Joined (连接): ○────────────────○ │ │ ○────────────────○ Butt (平头): │────────────────│ │ │ │────────────────│ Square (方形端): ┌────────────────┐ │ │ │ │ │ │ └────────────────┘ Round (圆形端): ╭────────────────╮ │ │ │ │ │ │ ╰────────────────╯ 16.5 AddPath/AddPaths 方法 16.5.1 添加路径 public void AddPath(Path64 path, JoinType joinType, EndType endType) { if (path.Count == 0) return; Paths64 paths = new Paths64(1) { path }; AddPaths(paths, joinType, endType); } public void AddPaths(Paths64 paths, JoinType joinType, EndType endType) { if (paths.Count == 0) return; _groupList.Add(new Group(paths, joinType, endType)); } 16.5.2 清除数据 public void Clear() { _groupList.Clear(); } 16.6 Execute 方法 16.6.1 执行偏移 public void Execute(double delta, Paths64 solution) { solution.Clear(); if (_groupList.Count == 0) return; _solution.Clear(); // 设置偏移量 _delta = delta; // 处理每个组 foreach (Group group in _groupList) { DoGroupOffset(group); } // 合并结果 if (_solution.Count > 0) { // 使用裁剪器合并可能重叠的区域 Clipper64 clipper = new Clipper64(); clipper.PreserveCollinear = _preserveCollinear; clipper.ReverseSolution = _reverseSolution; clipper.AddSubject(_solution); clipper.Execute(ClipType.Union, FillRule.Positive, solution); } } 16.6.2 Execute 重载 // 输出到 PolyTree64 public void Execute(double delta, PolyTree64 polytree) { Paths64 paths = new Paths64(); Execute(delta, paths); // 构建 PolyTree BuildPolyTree(paths, polytree); } // 浮点版本 public void Execute(double delta, PathsD solution) { Paths64 paths64 = new Paths64(); Execute(delta, paths64); // 转换为浮点 solution.Clear(); foreach (Path64 path in paths64) { PathD pathD = new PathD(path.Count); foreach (Point64 pt in path) { pathD.Add(new PointD(pt)); } solution.Add(pathD); } } 16.7 DoGroupOffset 16.7.1 组偏移处理 private void DoGroupOffset(Group group) { if (group.endType == EndType.Polygon) { // 闭合多边形 _groupDelta = group.pathsReversed ? -_delta : _delta; } else { // 开放路径 _groupDelta = Math.Abs(_delta); } _absGroupDelta = Math.Abs(_groupDelta); // 计算斜接限制 if (_miterLimit > 1) _mitLimSqr = 2 / (_miterLimit * _miterLimit); else _mitLimSqr = 2; // 计算圆弧步进 if (_absGroupDelta > 0) { double arcTol = _arcTolerance > 0 ? _arcTolerance : _absGroupDelta * 0.25; _stepsPerRad = Math.PI / Math.Acos(1 - arcTol / _absGroupDelta); _stepSin = Math.Sin(2 * Math.PI / _stepsPerRad); _stepCos = Math.Cos(2 * Math.PI / _stepsPerRad); if (_groupDelta < 0) _stepSin = -_stepSin; } // 处理每条路径 foreach (Path64 path in group.paths) { DoPath(path, group); } } 16.8 DoPath 路径偏移 16.8.1 处理单条路径 private void DoPath(Path64 path, Group group) { int pathLen = path.Count; if (pathLen < 2) return; // 构建法线向量 BuildNormals(path); Path64 result = new Path64(); if (group.endType == EndType.Polygon) { // 闭合多边形偏移 OffsetPolygon(path, result, group.joinType); } else if (group.endType == EndType.Joined) { // 连接的开放路径 OffsetOpenJoined(path, result, group.joinType); } else { // 开放路径 OffsetOpenPath(path, result, group.joinType, group.endType); } if (result.Count > 0) _solution.Add(result); } 16.8.2 构建法线 private void BuildNormals(Path64 path) { _normals.Clear(); int cnt = path.Count; for (int i = 0; i < cnt; i++) { int j = (i + 1) % cnt; double dx = path[j].X - path[i].X; double dy = path[j].Y - path[i].Y; double len = Math.Sqrt(dx * dx + dy * dy); if (len > 0) { dx /= len; dy /= len; } // 法线：垂直于边的单位向量 _normals.Add(new PointD(dy, -dx)); } } 16.9 偏移计算 16.9.1 OffsetPolygon private void OffsetPolygon(Path64 path, Path64 result, JoinType joinType) { int pathLen = path.Count; for (int i = 0, k = pathLen - 1; i < pathLen; k = i++) { // 偏移当前边 Point64 pt = new Point64( path[i].X + _normals[k].x * _groupDelta, path[i].Y + _normals[k].y * _groupDelta ); result.Add(pt); // 处理拐角 DoJoin(path, result, i, k, joinType); } } 16.9.2 DoJoin 拐角处理 private void DoJoin(Path64 path, Path64 result, int j, int k, JoinType joinType) { // 计算拐角角度 double cosA = _normals[k].x * _normals[j].x + _normals[k].y * _normals[j].y; // 凹角检测 double sinA = _normals[k].x * _normals[j].y - _normals[k].y * _normals[j].x; if (sinA * _groupDelta < 0) { // 凹角：添加交点 Point64 pt = GetIntersection(_normals[k], _normals[j], path[j], _groupDelta); result.Add(pt); return; } // 凸角：根据 JoinType 处理 switch (joinType) { case JoinType.Miter: DoMiter(path, result, j, k, cosA); break; case JoinType.Square: DoSquare(path, result, j, k); break; case JoinType.Bevel: DoBevel(path, result, j, k); break; case JoinType.Round: DoRound(path, result, j, k, sinA); break; } } 16.9.3 DoMiter private void DoMiter(Path64 path, Path64 result, int j, int k, double cosA) { // 检查是否超过斜接限制 double q = _groupDelta / (1 + cosA); if (q > _mitLimSqr * _absGroupDelta) { // 超过限制，使用斜角 DoBevel(path, result, j, k); } else { // 正常斜接 result.Add(new Point64( path[j].X + (_normals[k].x + _normals[j].x) * q, path[j].Y + (_normals[k].y + _normals[j].y) * q )); } } 16.9.4 DoRound private void DoRound(Path64 path, Path64 result, int j, int k, double sinA) { // 计算圆弧需要的步数 double a = Math.Atan2(sinA, _normals[k].x * _normals[j].x + _normals[k].y * _normals[j].y); int steps = Math.Max(2, (int)Math.Ceiling(_stepsPerRad * Math.Abs(a))); // 起始点 double x = _normals[k].x; double y = _normals[k].y; for (int i = 0; i < steps; i++) { result.Add(new Point64( path[j].X + x * _groupDelta, path[j].Y + y * _groupDelta )); // 旋转 double x2 = x * _stepCos - y * _stepSin; y = x * _stepSin + y * _stepCos; x = x2; } } 16.10 开放路径偏移 16.10.1 OffsetOpenPath private void OffsetOpenPath(Path64 path, Path64 result, JoinType joinType, EndType endType) { // 偏移正向 OffsetLine(path, result, joinType); // 处理终点 DoEndCap(path, result, endType, false); // 偏移反向 OffsetLineReverse(path, result, joinType); // 处理起点 DoEndCap(path, result, endType, true); } 16.10.2 DoEndCap 端点处理 private void DoEndCap(Path64 path, Path64 result, EndType endType, bool isStart) { int idx = isStart ? 0 : path.Count - 1; Point64 pt = path[idx]; PointD normal = isStart ? new PointD(-_normals[0].x, -_normals[0].y) : _normals[path.Count - 2]; switch (endType) { case EndType.Butt: // 平头：不添加额外点 result.Add(new Point64( pt.X + normal.x * _groupDelta, pt.Y + normal.y * _groupDelta )); break; case EndType.Square: // 方形端 result.Add(new Point64( pt.X + normal.x * _groupDelta - normal.y * _groupDelta, pt.Y + normal.y * _groupDelta + normal.x * _groupDelta )); result.Add(new Point64( pt.X - normal.x * _groupDelta - normal.y * _groupDelta, pt.Y - normal.y * _groupDelta + normal.x * _groupDelta )); break; case EndType.Round: // 圆形端 DoRoundEnd(pt, normal, result); break; } } 16.11 参数配置 16.11.1 MiterLimit public double MiterLimit { get => _miterLimit; set => _miterLimit = value > 0 ? value : 2.0; } MiterLimit 控制斜接角的最大延伸： MiterLimit = 2（默认）：角度约 60° 以下使用斜接 MiterLimit = 4：角度约 30° 以下使用斜接 MiterLimit = 1：总是使用斜角 16.11.2 ArcTolerance public double ArcTolerance { get => _arcTolerance; set => _arcTolerance = value > 0 ? value : 0.25; } ArcTolerance 控制圆弧的精度： 值越小，圆弧越平滑 值越大，圆弧越粗糙 默认 0.25，即误差 0.25 单位 16.12 使用示例 16.12.1 基本使用 ClipperOffset co = new ClipperOffset(); // 添加多边形 Path64 polygon = new Path64 { new Point64(0, 0), new Point64(100, 0), new Point64(100, 100), new Point64(0, 100) }; co.AddPath(polygon, JoinType.Round, EndType.Polygon); // 执行膨胀 10 单位 Paths64 result = new Paths64(); co.Execute(10, result); // 执行收缩 5 单位 co.Clear(); co.AddPaths(result, JoinType.Round, EndType.Polygon); Paths64 shrunk = new Paths64(); co.Execute(-5, shrunk); 16.12.2 开放路径 ClipperOffset co = new ClipperOffset(); Path64 line = new Path64 { new Point64(0, 0), new Point64(100, 50), new Point64(200, 0) }; // 圆角端点 co.AddPath(line, JoinType.Round, EndType.Round); Paths64 result = new Paths64(); co.Execute(10, result); 16.13 本章小结 ClipperOffset 提供了强大的路径偏移功能： JoinType：四种拐角连接方式 EndType：五种端点处理方式 参数控制：MiterLimit 和 ArcTolerance 自动合并：使用裁剪器合并重叠区域 合理配置参数可以满足各种偏移需求。 上一章：填充规则详解 | 返回目录 | 下一章：RectClip矩形裁剪优化