在GIS的世界里，矢量数据以其独特的空间关系和丰富的属性信息，成为了地理分析不可或缺的工具。然而，随着版本的迭代，矢量数据的读写也变得越来越复杂。今天，就让我们通过一个生动的示例，探索如何使用GDAL/OGR库，轻松实现从DXF文件到SHP文件的矢量转换。

一、读取DXF文件中的线（环）特征

首先，我们来看一个具体的例子。假设我们有一个DXF文件，里面包含了线（环）特征。我们的目标是将这些线特征转换为面特征，并保存在一个新的SHP文件中。

# include <iostream>
# include <gdal/ogrsf_frmts.h>

using namespace std;

bool ReadDXF(string filePath, vector<vector<OGRPoint>>& vertexPoint)
{
    GDALDataset *poDS = (GDALDataset*)GDALOpenEx(filePath.c_str(), GDAL_OF_VECTOR, NULL, NULL, NULL);
    if (!poDS)
    {
        printf("无法读取该文件，试检查格式是否正确！");
        return false;
    }
    if (poDS->GetLayerCount() < 1)
    {
        printf("该文件的层数小于1，试检查格式是否正确！");
        return false;
    }

    OGRLayer *poLayer = poDS->GetLayer(0);
    poLayer->ResetReading();
    OGRFeature *poFeature;
    while ((poFeature = poLayer->GetNextFeature()) != NULL)
    {
        OGRGeometry *pGeo = poFeature->GetGeometryRef();
        OGRwkbGeometryType pGeoType = pGeo->getGeometryType();
        if (pGeoType == wkbLineString || pGeoType == wkbLineString25D)
        {
            OGRLinearRing *pCurve = (OGRLinearRing*)pGeo;
            if (pCurve->getNumPoints() < 1)
            {
                continue;
            }

            vector<OGRPoint> pl;
            for (int i = 0; i < pCurve->getNumPoints(); i++)
            {
                OGRPoint point;
                pCurve->getPoint(i, &point);
                pl.push_back(point);
            }
            vertexPoint.push_back(pl);
        }
    }

    GDALClose(poDS);
    poDS = nullptr;
    return true;
}

二、将线特征转换为面特征

接下来，我们需要将这些线特征转换为面特征。这一步骤通常涉及到对几何对象的合并和简化。

bool WriteShp(string filePath, vector<vector<OGRPoint>> vertexPoint)
{
    GDALDriver* driver = GetGDALDriverManager()->GetDriverByName("ESRI Shapefile");
    if (!driver)
    {
        printf("Get Driver ESRI Shapefile Error！");
        return false;
    }

    GDALDataset* dataset = driver->Create(filePath.c_str(), 0, 0, 0, GDT_Unknown, NULL);
    OGRLayer* poLayer = dataset->CreateLayer("houseType", NULL, wkbPolygon, NULL);

    {
        OGRFieldDefn oField1("名称", OFTString);
        oField1.SetWidth(8);
        if (poLayer->CreateField(&oField1) != OGRERR_NONE)
        {
            printf("Creating Name field failed.");
            return FALSE;
        }

        OGRFieldDefn oField2("面积", OFTReal);
        oField2.SetPrecision(3);
        if (poLayer->CreateField(&oField2) != OGRERR_NONE)
        {
            printf("Creating Area field failed.");
            return FALSE;
        }

        OGRFieldDefn oField3("结点数", OFTInteger);
        if (poLayer->CreateField(&oField3) != OGRERR_NONE)
        {
            printf("Creating Node count field failed.");
            return FALSE;
        }
    }

    for (auto& iter : vertexPoint)
    {
        OGRFeature *poFeature = new OGRFeature(poLayer->GetLayerDefn());
        OGRLinearRing ogrring;
        int pNum = (int)iter.size();
        ogrring.setNumPoints(pNum);
        for (int i = 0; i < iter.size(); i++)
        {
            ogrring.setPoint(i, iter[i].getX(), iter[i].getY(), iter[i].getZ());
        }
        OGRPolygon polygon;
        polygon.addRing(&ogrring);
        poFeature->SetGeometry(&polygon);
        poFeature->SetField("名称", "多边形");
        poFeature->SetField("面积", polygon.get_Area());
        poFeature->SetField("结点数", pNum);
        if (poLayer->CreateFeature(poFeature) != OGRERR_NONE)
        {
            printf("Failed to create feature in shapefile.");
            return false;
        }
    }

    GDALClose(dataset);
    dataset = nullptr;
    return true;
}

三、主函数

最后，我们将这些功能整合到一个主函数中，以便在实际应用中使用。

int main()
{
    GDALAllRegister();
    CPLSetConfigOption("GDAL_FILENAME_IS_UTF8", "NO");
    CPLSetConfigOption("SHAPE_ENCODING", "");

    string filePath = "D:/2.dxf";
    vector<vector<OGRPoint>> vertexPoint;
    if (!ReadDXF(filePath, vertexPoint))
    {
        return 1;
    }

    string newPath = "C:/Users/charlee/Desktop/SHP/dst.shp";
    WriteShp(newPath, vertexPoint);
    return 0;
}

通过这个示例，我们不仅学会了如何使用GDAL/OGR库读取和写入矢量数据，还掌握了如何将线特征转换为面特征，并保存在SHP文件中。希望这个示例能帮助你在实际工作中更加得心应手地处理矢量数据。