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问题：进行拓扑运算（ITopologicalOperator.SymmetricDifference）的时候报错“异常来自 HRESULT:0x80040218”
解决方案：经网上查阅资料，发现是输入图形未经简化处理所致。对于进行拓扑运算的图形，都要进行Simplify处理。完善代码如下：
1 ITopologicalOperator topoOpr = bigPolygon as ITopologicalOperator; 2 topoOpr.Simplify(); 3 (smallPolygon as ITopologicalOperator).Simplify(); 4 IPolygon ringpoly = topoOpr.SymmetricDifference(smallPolygon as IGeometry) as IPolygon;
参考：http://gis-conquer.blog.sohu.com/244181846.html
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原文地址：http://www.cnblogs.com/lettet/p/4562755.html
