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我有三角点，我想使用选定的三角形来生成多边形。当我使用地理坐标时，我自然会选择 OGR 来执行矢量处理。

因此，在定义了我的 OGRLayer（作为 OGRPolygon）之后，我为之前选择的每个三角形创建了一个 OGRPolygon（通过 OGRLinearRing），并尝试将它们合并到一个多边形中：

OGRPolygon ogrmerged;
for(int i=0; i<triangles.size(); i++){
    OGRLinearRing ogrring;
    ogrring.addPoint( triangles[i].a.x, triangles[i].a.y );
    ogrring.addPoint( triangles[i].b.x, triangles[i].b.y );
    ogrring.addPoint( triangles[i].c.x, triangles[i].c.y );
    ogrring.closeRings();
    OGRPolygon ogrtriangle;
    ogrtriangle.addRing( &ogrring );
    ogrmerged = *( (OGRPolygon*) ogrmerged.Union( &ogrtriangle ) );
}

结果是崩溃或空多边形...

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1 回答 1

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由于Union返回一个新分配的对象，您需要确保清理旧对象。

OGRPolygon* pOgrMerged = new OGRPolygon();
for(int i=0; i<triangles.size(); i++){
    OGRLinearRing ogrring;
    ogrring.addPoint( triangles[i].a.x, triangles[i].a.y );
    ogrring.addPoint( triangles[i].b.x, triangles[i].b.y );
    ogrring.addPoint( triangles[i].c.x, triangles[i].c.y );
    ogrring.closeRings();
    OGRPolygon ogrtriangle;
    ogrtriangle.addRing( &ogrring );
    OGRPolygon* pTemp = static_cast<OGRPolygon*>(pOgrMerged->Union(&ogrtriangle));
    if (pTemp != NULL) // If you are using C++11 you could check for nullptr)
    {
        delete pOgrMerged;
        pOgrMerged = pTemp;
    }
    else
    {
        // Handle the case where the merge resulted in an error. It may be because
        // the polygons didn't overlap or something like that, check the docs for OGR
    }
}

// Do what you need to do with pOgrMerged and then return it or delete it (do not
// delete it if you are going to return it
delete pOgrMerged;

我知道这段代码使用的是原始指针。我不知道您是否使用 C++11 或 boost 或其他库，但我建议使用 unique_ptr/shared_ptr 之类的东西包装原始指针，或者如果您必须使用 auto_ptr。这样你就不会泄漏对象。

使用unique_ptr的相同代码：

std::uniqe_ptr<OGRPolygon> pOgrMerged(new OGRPolygon());
for(int i=0; i<triangles.size(); i++){
    OGRLinearRing ogrring;
    ogrring.addPoint( triangles[i].a.x, triangles[i].a.y );
    ogrring.addPoint( triangles[i].b.x, triangles[i].b.y );
    ogrring.addPoint( triangles[i].c.x, triangles[i].c.y );
    ogrring.closeRings();
    OGRPolygon ogrtriangle;
    ogrtriangle.addRing( &ogrring );
    OGRPolygon* pTemp = static_cast<OGRPolygon*>(pOgrMerged->Union(&ogrtriangle));
    if (pTemp != NULL) // If you are using C++11 you could check for nullptr)
    {
        pOgrMerged.reset(pTemp);
    }
    else
    {
        // Handle the case where the merge resulted in an error. It may be because
        // the polygons didn't overlap or something like that, check the docs for OGR
    }
}
于 2012-10-22T17:16:55.177 回答