Engine中实现平头缓冲

【解决办法】：
Engine中提供了生成平头缓冲的接口，利用IBufferConstruction和IBufferConstructionProperties接口，设置IBufferConstructionProperties.EndOption为esriBufferFlat即为平头缓冲。参考代码：

IGeometry polyline = feature.ShapeCopy; 

IEnumGeometry enumGeometry = new GeometryBagClass(); 

IGeometryCollection geometryCollection = enumGeometry as IGeometryCollection; 

geometryCollection.AddGeometry(polyline); 

IBufferConstruction bufferContruction = new BufferConstructionClass(); 

IBufferConstructionProperties bufferProper = bufferContruction as IBufferConstructionProperties; 

bufferProper.EndOption = esriBufferConstructionEndEnum.esriBufferFlat; 

IGeometryCollection outputBuffers = new GeometryBagClass(); 

bufferContruction.ConstructBuffers(enumGeometry, 200, outputBuffers);