public void PprArc()
{
//准备工作
Document doc = Application.DocumentManager.MdiActiveDocument;
Database db = doc.Database;
Editor ed = doc.Editor;
Transaction trans = db.TransactionManager.StartTransaction();
BlockTable bt = trans.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable;
BlockTableRecord btr = trans.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord;
PromptPointOptions ppo = new PromptPointOptions("");
PromptPointResult ppr;
Point3d temp = new Point3d();
Point2d p1, p2;
//获取两个点
ppo.Message = "\n请输入第一个点：";
do
{
ppr = ed.GetPoint(ppo);
temp = ppr.Value;
p1 = new Point2d(temp.X, temp.Y);
} while (ppr.Status != PromptStatus.OK);
ppo.Message = "\n请输入第二个点：";
do
{
ppr = ed.GetPoint(ppo);
temp = ppr.Value;
p2 = new Point2d(temp.X, temp.Y);
} while (ppr.Status != PromptStatus.OK);
double L = p1.GetDistanceTo(p2);
double R = 0;
//获取半径
do
{//避免出现半径比弦长一半还小的情况出现
PromptDoubleOptions pdo = new PromptDoubleOptions("\n最后，请输入半径：");
PromptDoubleResult pdr = ed.GetDouble(pdo);
if (pdr.Status == PromptStatus.OK)
{
R = pdr.Value;
}
} while (R < L / 2);
double H = R - Math.Sqrt(R * R - L * L / 4);
Polyline poly = new Polyline();
poly.AddVertexAt(0, p1, 2 * H / L, 0, 0);
poly.AddVertexAt(1, p2, 0, 0, 0);
btr.AppendEntity(poly);
trans.AddNewlyCreatedDBObject(poly, true);
trans.Commit();
trans.Dispose();
}