GDAL 获取多边形OGRPolygon的方法

来源：互联网发布：域名解析软件的作用编辑：程序博客网时间：2024/06/06 06:49

GIS是一门很大的学问，就拿怎么在SHP文件中获得一个多边形来说，我看了很多的人的博客都是这样的：

OGRFeature *cityOutsideBuildingPoFeature;while ((cityOutsideBuildingPoFeature = mLayer->GetNextFeature()) != NULL){OGRGeometry *rdPoGeometry = cityOutsideBuildingPoFeature->GetGeometryRef();if (rdPoGeometry != NULL){OGRwkbGeometryType pGeoType = rdPoGeometry->getGeometryType();OGRPolygon *rdPolygon;if (pGeoType == wkbPolygon)//这里就是多边形判断{rdPolygon = (OGRPolygon*)rdPoGeometry->clone();}else if (pGeoType == wkbMultiPolygon)  //这里就是带空洞多边形判断{OGRMultiPolygon * multiPolygon = (OGRMultiPolygon *)rdPoGeometry;multiPolygon->closeRings();OGRGeometry *FirstGeometry = NULL;FirstGeometry = multiPolygon->getGeometryRef(0);rdPolygon = (OGRPolygon *)FirstGeometry;}}OGRFeature::DestroyFeature(cityOutsideBuildingPoFeature);}

我觉得在获得多边形外轮廓时，感觉有点多余了，最终获得的也只是多个多边形中的第一个多边形而已，这不可能达到需求，那怎么获得整个多边形的多轮廓呢，如下：

OGRFeature *cityOutsideBuildingPoFeature;while ((cityOutsideBuildingPoFeature = _mOCityBuildingLayerOper->mLayer->GetNextFeature()) != NULL){OGRGeometry *rdPoGeometry = cityOutsideBuildingPoFeature->GetGeometryRef();if (rdPoGeometry != NULL){OGRwkbGeometryType pGeoType = rdPoGeometry->getGeometryType();OGRPolygon *rdPolygon;if (pGeoType == wkbPolygon)//这里就是多边形判断{rdPolygon = (OGRPolygon*)rdPoGeometry->clone();}else if (pGeoType == wkbMultiPolygon)  //这里就是带空洞多边形判断{OGRMultiPolygon * multiPolygon = (OGRMultiPolygon *)rdPoGeometry;int num = multiPolygon->getNumGeometries();rdPolygon = (OGRPolygon *)multiPolygon->getGeometryRef(0);for (int i = 1; i < num; i++){OGRPolygon *mOGRPolygon = (OGRPolygon *)multiPolygon->getGeometryRef(i);rdPolygon = (OGRPolygon *)rdPolygon->Union(mOGRPolygon);}}}OGRFeature::DestroyFeature(cityOutsideBuildingPoFeature);}

由上代码可以看出，我们需要遍历wkbMultiPolygon，然后将所有多边形求并集，这样就可以获取到整个多边形的外轮廓了

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