线缓冲区边界生成算法【转】
/***********************************************************************
* 文档作者：dxj
* 创建时间：2010.3.7 20:17
* 文档说明：
* 本文件是线缓冲区边界生成算法的C#实现。
**********************************************************************/
using System;
using System.Collections.Generic;
using System.Text;
using DXJ.Teresa.GIS.GeoObject;
using DXJ.Teresa.GIS.Utility;
namespace DXJ.Teresa.GIS.Buffer
{
/// <summary>
/// 线缓冲区边界生成算法
/// </summary>
public class PolylineBuffer
{
/// <summary>
/// 根据给定的一系列有顺序的坐标，逆时针生成缓冲区的边界坐标。
/// </summary>
/// <param name="strPolyLineCoords">一系列有顺序的坐标</param>
/// <param name="radius">缓冲区半径</param>
/// <returns>缓冲区的边界坐标</returns>
public static string GetBufferEdgeCoords(string strPolyLineCoords, double radius)
{
//参数处理
if (strPolyLineCoords.Trim().Length < 1) return "";
string[] strCoords = strPolyLineCoords.Split(new char[] { ';' });
List<Coordinate> coords = new List<Coordinate>();
foreach (string coord in strCoords)
{
coords.Add(new Coordinate(coord));
}
//分别生成左侧和右侧的缓冲区边界点坐标串
string leftBufferCoords = GetLeftBufferEdgeCoords(coords, radius);
coords.Reverse();
string rightBufferCoords = GetLeftBufferEdgeCoords(coords, radius);
return leftBufferCoords + ";" + rightBufferCoords;
}
#region Private Methods
/// <summary>
/// 根据给定的一系列有顺序的坐标，逆时针生成轴线左侧的缓冲区边界点
/// </summary>
/// <param name="coords">一系列有顺序的坐标</param>
/// <param name="radius">缓冲区半径</param>
/// <returns>缓冲区的边界坐标</returns>
private static string GetLeftBufferEdgeCoords(IList<Coordinate> coords, double radius)
{
//参数处理
if (coords.Count < 1) return "";
else if (coords.Count < 2) return PointBuffer.GetBufferEdgeCoords(coords[0], radius);
//计算时所需变量
double alpha = 0.0;//向量绕起始点沿顺时针方向旋转到X轴正半轴所扫过的角度
double delta = 0.0;//前后线段所形成的向量之间的夹角
double l = 0.0;//前后线段所形成的向量的叉积
//辅助变量
StringBuilder strCoords = new StringBuilder();
double startRadian = 0.0;
double endRadian = 0.0;
double beta = 0.0;
double x = 0.0, y = 0.0;
//第一节点的缓冲区
{
alpha = MathTool.GetQuadrantAngle(coords[0], coords[1]);
startRadian = alpha + Math.PI;
endRadian = alpha + (3 * Math.PI) / 2;
strCoords.Append(GetBufferCoordsByRadian(coords[0], startRadian, endRadian, radius));
}
//中间节点
for (int i = 1; i < coords.Count - 1; i++)
{
alpha = MathTool.GetQuadrantAngle(coords[i], coords[i + 1]);
delta = MathTool.GetIncludedAngel(coords[i - 1], coords[i], coords[i + 1]);
l = GetVectorProduct(coords[i - 1], coords[i], coords[i + 1]);
if (l > 0)
{
startRadian = alpha + (3 * Math.PI) / 2 - delta;
endRadian = alpha + (3 * Math.PI) / 2;
if (strCoords.Length > 0) strCoords.Append(";");
strCoords.Append(GetBufferCoordsByRadian(coords[i], startRadian, endRadian, radius));
}
else if (l < 0)
{
beta = alpha - (Math.PI - delta) / 2;
x = coords[i].X + radius * Math.Cos(beta);
y = coords[i].Y + radius * Math.Sin(beta);
if (strCoords.Length > 0) strCoords.Append(";");
strCoords.Append(x.ToString() + "," + y.ToString());
}
}
//最后一个点
{
alpha = MathTool.GetQuadrantAngle(coords[coords.Count - 2], coords[coords.Count - 1]);
startRadian = alpha + (3 * Math.PI) / 2;
endRadian = alpha + 2 * Math.PI;
if (strCoords.Length > 0) strCoords.Append(";");
strCoords.Append(GetBufferCoordsByRadian(coords[coords.Count - 1], startRadian, endRadian, radius));
}
return strCoords.ToString();
}
/// <summary>
/// 获取指定弧度范围之间的缓冲区圆弧拟合边界点
/// </summary>
/// <param name="center">指定拟合圆弧的原点</param>
/// <param name="startRadian">开始弧度</param>
/// <param name="endRadian">结束弧度</param>
/// <param name="radius">缓冲区半径</param>
/// <returns>缓冲区的边界坐标</returns>
private static string GetBufferCoordsByRadian(Coordinate center, double startRadian, double endRadian, double radius)
{
double gamma = Math.PI / 6;
StringBuilder strCoords = new StringBuilder();
double x = 0.0, y = 0.0;
for (double phi = startRadian; phi <= endRadian + 0.000000000000001; phi += gamma)
{
x = center.X + radius * Math.Cos(phi);
y = center.Y + radius * Math.Sin(phi);
if (strCoords.Length > 0) strCoords.Append(";");
strCoords.Append(x.ToString() + "," + y.ToString());
}
return strCoords.ToString();
}
/// <summary>
/// 获取相邻三个点所形成的两个向量的交叉乘积
/// </summary>
/// <param name="preCoord">第一个节点坐标</param>
/// <param name="midCoord">第二个节点坐标</param>
/// <param name="nextCoord">第三个节点坐标</param>
/// <returns>相邻三个点所形成的两个向量的交叉乘积</returns>
private static double GetVectorProduct(Coordinate preCoord, Coordinate midCoord, Coordinate nextCoord)
{
return (midCoord.X - preCoord.X) * (nextCoord.Y - midCoord.Y) - (nextCoord.X - midCoord.X) * (midCoord.Y - preCoord.Y);
}
#endregion
}
}
