Question

我正在c ++中使用opencv从地理空间图像中提取一组2D点。使用这些点作为顶点，我想创建一个多边形ESRI shapefile。

Gdal api教程（https://gdal.org/1.11/ogr/ogr_apitut.html）仅包含有关如何创建点和线串shapefile的示例。像“ OGR_G_AddPoint_2D”之类的功能不适用于多边形类型shapefile。

我有一个功能，可以在点图层中添加一个点，并且效果很好。

void addPoint(OGRLayerH hLayer, long x, long y, const char *szName){  
    OGRFeatureH hFeature;
    hFeature = OGR_F_Create( OGR_L_GetLayerDefn( hLayer ) );
    OGR_F_SetFieldString( hFeature, OGR_F_GetFieldIndex(hFeature, "Name"), szName );

    OGRGeometryH hPt;
    hPt = OGR_G_CreateGeometry(wkbPoint);
    OGR_G_SetPoint_2D(hPt, 0, x, y);
    OGR_F_SetGeometry( hFeature, hPt );
    OGR_G_DestroyGeometry(hPt);

    if( OGR_L_CreateFeature( hLayer, hFeature ) != OGRERR_NONE ){
       printf( "Failed to create feature in shapefile.\n" );
       exit(1);
    }
    OGR_F_Destroy( hFeature );
};

试图将其更改为多边形。没有错误打印，但没有保存shapefile。

void addPolygon(OGRLayerH hLayer, double *x, double *y, const char *szName){  
    OGRFeatureH hFeature;
    hFeature = OGR_F_Create( OGR_L_GetLayerDefn( hLayer ) );
    OGR_F_SetFieldString(hFeature, OGR_F_GetFieldIndex(hFeature, "Name"), szName);

    OGRGeometryH hGeo;
    hGeo = OGR_G_CreateGeometry(wkbLineString);

    cout << "Performing for loop" << endl;
    for (int i=0; i < 4; i++){
        OGR_G_SetPoint_2D(hGeo, 0, x[i], y[i]);
    }
    OGR_G_CloseRings(hGeo);
    hGeo = OGR_G_ForceToPolygon(hGeo);

    if( OGR_L_CreateFeature( hLayer, hFeature ) != OGRERR_NONE ){
       printf( "Failed to create feature in shapefile.\n" );
       exit(1);
    }
    OGR_F_Destroy( hFeature );
    return;
};

Answer 1

函数OGR_G_SetPoint_2D需要该点的索引i。如果所有索引均为0，它将绘制一个点而不是一个多边形。这对我有用：

void addPolygon(OGRLayerH hLayer, double *x, double *y, int n, const char *szName)
{  OGRFeatureH hFeature=OGR_F_Create(OGR_L_GetLayerDefn(hLayer));
   OGR_F_SetFieldString(hFeature,OGR_F_GetFieldIndex(hFeature,"Name"),szName);
   OGRGeometryH hGeo=OGR_G_CreateGeometry(wkbLinearRing);
   printf("Performing LinearRing of %d vertices\n",n);
   for(int i=0;i<n;i++) { OGR_G_SetPoint_2D(hGeo,i,x[i],y[i]); }
   OGR_G_CloseRings(hGeo);
   hGeo=OGR_G_ForceToPolygon(hGeo);
   OGR_F_SetGeometry(hFeature,hGeo);
   OGR_G_DestroyGeometry(hGeo);
   if(OGR_L_CreateFeature(hLayer,hFeature) != OGRERR_NONE)
   {  printf("Failed to create feature in shapefile.\n"); exit(1); }
   OGR_F_Destroy(hFeature);
   return;
}

如何在C ++中创建多边形ESRI shapefile？

1 个答案: