2021-07-05C＃/CAD二次开发创建圆弧（4）

代码如下：
ArcExam.cs

using System;
using System.Collections.Generic;
using System.Text;
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.Geometry;

namespace _2图形创建
{
    
    public class ArcExam
    {
    
        [CommandMethod("ArcDemo")]
        public void ArcDemo()
        {
    
            Arc arc1 = new Arc();
            arc1.Center = new Point3d(0, 0, 0);
            arc1.StartAngle = 0;
            arc1.EndAngle = Math.PI;
            arc1.Radius = 100;
            double startDegree = 45;
            Arc arc2 = new Arc(new Point3d(500, 500, 0), 20,BaseTool.DegreeToAngle(startDegree), Math.PI);
            Arc arc3 = new Arc(new Point3d(100, 100, 0), new Vector3d(0, 0, 1), 20, Math.PI / 4, Math.PI / 2);

            Database db = HostApplicationServices.WorkingDatabase;
            AddEnityTool.AddEnityToModelSpace(db, arc1,arc2,arc3);
        }
    }
}

代码解析：
以上代码基本是为了介绍CAD里圆弧方法的用法

Arc arc1 = new Arc();
arc1.Center = new Point3d(0, 0, 0);
arc1.StartAngle = 0;
arc1.EndAngle = Math.PI;
arc1.Radius = 100;

Center 圆心坐标；StartAngle 开始弧度；EndAngle 结束弧度；Radius 半径；
注意此处的属性是弧度

double startDegree = 45;
Arc arc2 = new Arc(new Point3d(500, 500, 0), 20,BaseTool.DegreeToAngle(startDegree), Math.PI);

这里也是弧度值，我们通过先前创建的角度转弧度方法将45度转换为弧度
从左至右，依次是圆心、半径、开始弧度、结束弧度。
arc3涉及Vector3d，我画二维图，用不到，指的是笛卡尔坐标。

三点绘制圆弧
代码如下：

using System;
using System.Collections.Generic;
using System.Text;
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.Geometry;

namespace _2图形创建
{
    
    public class ArcExam
    {
    
        [CommandMethod("ArcDemo")]
        public void ArcDemo()
        {
    
            Database db = HostApplicationServices.WorkingDatabase;
            Point3d startPoint = new Point3d(100, 100, 0);
            Point3d endPoint = new Point3d(200, 200, 0);
            Point3d pointOnArc = new Point3d(150, 100, 0);
            CircularArc3d cArc = new CircularArc3d(startPoint,pointOnArc,endPoint);

            double radius = cArc.Radius;
            Point3d center = cArc.Center;
            Vector3d cs = center.GetVectorTo(startPoint);
            Vector3d ce = center.GetVectorTo(endPoint);
            Vector3d xvector = new Vector3d(1, 0, 0);
            double startAngle = cs.Y > 0 ? xvector.GetAngleTo(cs) : -xvector.GetAngleTo(cs);
            double endAngle = ce.Y > 0 ? xvector.GetAngleTo(ce) : -xvector.GetAngleTo(ce);
            Arc arc = new Arc(center,radius,startAngle,endAngle);
            AddEnityTool.AddEnityToModelSpace(db, arc);
        }
    }
}

代码解释：

Database db = HostApplicationServices.WorkingDatabase;
Point3d startPoint = new Point3d(100, 100, 0);
Point3d endPoint = new Point3d(200, 200, 0);
Point3d pointOnArc = new Point3d(150, 100, 0);
CircularArc3d cArc = new CircularArc3d(startPoint,pointOnArc,endPoint);

创建了三个点，然后通过CircularArc3d方法创建了一个圆弧对象

尝试用ARC方法实现三点画圆

double radius = cArc.Radius;
Point3d center = cArc.Center;

首先获取上面圆弧的半径和中心点。

Vector3d cs = center.GetVectorTo(startPoint);
Vector3d ce = center.GetVectorTo(endPoint);

此处代码可以通过GetVectorTo方法分别获得圆心到两个点的向量。

Vector3d xvector = new Vector3d(1, 0, 0);

创建一个X方向的单位向量

double startAngle = cs.Y > 0 ? xvector.GetAngleTo(cs) : -xvector.GetAngleTo(cs);
double endAngle = ce.Y > 0 ? xvector.GetAngleTo(ce) : -xvector.GetAngleTo(ce);

通过GetAngleTo获得两个向量之间的夹角（弧度值），因为GetAngleTo获得的夹角（此为弧度制）都为正值，通过判断来取其负值，即可画出这个圆弧

如上图，红线、绿线与X轴的夹角都是42°，GetAngleTo获得的值都是42°的弧度值（正值），所以为了区分，做一个判断，startPoint或endPoint的Y坐标为负值时返回一个负的弧度值。

对上面创建圆弧的代码页封装到AddEnityTool.cs中

首先将判断X轴夹角是在X轴上方还是下方的代码封装到BaseTool.cs中

        /// <summary>
        /// 获取两点成直线到X轴之间的角度（有正负）
        /// </summary>
        /// <param name="startPoint">起点</param>
        /// <param name="endPoint">终点</param>
        /// <returns></returns>
        public static double GetAngleToXaxis(Point3d startPoint, Point3d endPoint) 
        {
    
            //声明一个与X轴平行的向量
            Vector3d temp = new Vector3d(1, 0, 0);
            //获取起点到终点的向量
            Vector3d VsToe = startPoint.GetVectorTo(endPoint);
            return VsToe.Y > 0 ? temp.GetAngleTo(VsToe) : -temp.GetAngleTo(VsToe);
        }

封装为GetAngleToXaxis方法

未防止给的三个点在同一条直线上，也加了一个判断条件封装到BaseTool.cs中

        /// <summary>
        /// 判断三点是否在同一直线上
        /// </summary>
        /// <param name="firstPoint">第一个点</param>
        /// <param name="secondPoint">第二个点</param>
        /// <param name="thirdPoint">第三个点</param>
        /// <returns></returns>
        public static bool IsOnOneLine(Point3d firstPoint, Point3d secondPoint, Point3d thirdPoint)
        {
    
            Vector3d v21 = secondPoint.GetVectorTo(firstPoint);
            Vector3d v23 = secondPoint.GetVectorTo(thirdPoint);
            if (v21.GetAngleTo(v23) == 0 || v21.GetAngleTo(v23) == Math.PI)
            {
    
                return true;
            }
            else
            {
    
                return false;
            }
        }

封装为IsOnOneLine方法

AddEnityTool.cs中代码

        /// <summary>
        /// 通过三点创建圆弧
        /// </summary>
        /// <param name="db">图形数据库</param>
        /// <param name="startPoint">起点</param>
        /// <param name="pointOnArc">圆弧上的点</param>
        /// <param name="endPoint">终点</param>
        /// <returns></returns>
		public static object AddArcToModelSpace(Database db, Point3d startPoint, Point3d pointOnArc, Point3d endPoint)
        {
    
            //先判断三点是否在同一直线上
            if (BaseTool.IsOnOneLine(startPoint, pointOnArc, endPoint))
            {
    
                return ObjectId.Null;
            }
            CircularArc3d cArc = new CircularArc3d(startPoint, pointOnArc, endPoint);
            Arc arc = new Arc(cArc.Center, cArc.Radius, BaseTool.GetAngleToXaxis(cArc.Center,startPoint), BaseTool.GetAngleToXaxis(cArc.Center,endPoint));
            //加入图形数据库
            return AddEnityTool.AddEnityToModelSpace(db,arc);
        }

通过通过圆心、起点、夹角绘制圆（AddEnityTool.cs）

        /// <summary>
        /// 通过圆心、起点、夹角绘制圆
        /// </summary>
        /// <param name="db">图形数据库</param>
        /// <param name="center">圆心</param>
        /// <param name="startPoint">起点</param>
        /// <param name="degree">夹角</param>
        /// <returns>ObjectId</returns>
        public static ObjectId AddArcToModelSpace(Database db, Point3d center, Point3d startPoint, double degree) 
        {
    
            //获取半径
            double radius = BaseTool.GetDistanceBetweenTwoPoint(center, startPoint);
            //获取起点角度
            double startAngle = BaseTool.GetAngleToXaxis(center, startPoint);
            //声明圆弧对象
            Arc arc = new Arc(center, radius, startAngle, startAngle + BaseTool.DegreeToAngle(degree));
            return AddEnityTool.AddEnityToModelSpace(db, arc);
        }

获取半径的代码如下（BaseTool.cs）

        /// <summary>
        /// 获取两点之间的距离
        /// </summary>
        /// <param name="point1"></param>
        /// <param name="point2"></param>
        /// <returns></returns>
        public static double GetDistanceBetweenTwoPoint(Point3d point1, Point3d point2) 
        {
    
            return Math.Sqrt((point1.X - point2.X) * (point1.X - point2.X) + (point1.Y - point2.Y) * (point1.Y - point2.Y) + (point1.Z - point2.Z) * (point1.Z - point2.Z));
        }