point\polyline\polygon的转化（转）

首先你要明白Polyline是由path对象构成，Polygon是由ring对象构成，因此实现polyline向polygon的转换，思路如下：
1.提取polyline中的所有path对象
2.将path对象转换成ring对象，由于IRing继承自IPath，因此该转换是合理的
3.利用IGeometryCollection.AddGeometry添加ring对象，构成polygon
示例如下：

1.       //cast the polyline object to the polygon
2.             ISegmentCollection pRing;
3.             IGeometryCollection pPolygon = new PolygonClass();
4.             object o = Type.Missing;
5.             for (int i = 0; i < pPolyline.GeometryCount;i++ )
6.             {
7.                 pRing = new RingClass();
8.                 pRing.AddSegmentCollection(pPolyline.get_Geometry(i) as ISegmentCollection);
9.                 pPolygon.AddGeometry(pRing as IGeometry, ref o, ref o);
10.             }

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point转为polyline，思路如下：
polyline是由path构成，path是由segment构成，因此首先构建segment对象，然后利用ISegmentCollection.AddSegment构造path，最后利用IGeometryCollection.AddGeometry构造polyline
示例如下：

1.       IPoint point1 = new PointClass();
2.             point1.PutCoords(100, 200);
3.             IPoint point2 = new PointClass();
4.             point2.PutCoords(600, 700);
5.             IPoint point3 = new PointClass();
6.             point3.PutCoords(450, 800);
7.             [color=Blue]//new a line object[/color]
8.             ILine pLine = new LineClass();
9.             object o = Type.Missing;
10.             pLine.PutCoords(point1, point2);
11.             [color=Blue]//new a path[/color]
12.             ISegmentCollection pPath = new PathClass();
13.             pPath.AddSegment((ISegment)pLine, ref o, ref o);
14.             pLine = new LineClass();
15.             pLine.PutCoords(point2, point3);
16.             pPath.AddSegment((ISegment)pLine, ref o, ref o);
17.             [color=Blue]//new a polyline[/color]
18.             IGeometryCollection pPolyline = new PolylineClass();
19.             pPolyline.AddGeometry((IGeometry)pPath, ref o, ref o);

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