GDAL(Geospatial Data AbstractionLibrary)是一個在X/MIT許可協議下的開源柵格空間數據轉換庫。它利用抽象數據模型來表達所支持的各種文件格式。它還有一系列命令行工具來進行數據轉換和處理。
本文將使用GDAL/OGR庫讀寫Postgresql數據庫中的表，代碼執行環境在ubuntu12.04，
直接上代碼
#include "/usr/include/gdal/ogrsf_frmts.h"
#include "/usr/include/gdal/ogr_feature.h"
#include "/usr/include/gdal/ogr_geometry.h"
#include "/usr/include/gdal/gdal_priv.h"
///////////////////////////////
//使用OGR讀Postgresql
///////////////////////////////
int getFeature( vector<RoadRec>& RoadList //RoadRec是自定義數據結構
)
{
OGRRegisterAll();
const char* filepath =
"PG:dbname=test host=172.0.0.1 port=5432 user=postgres password=postgres";
const char* drivename = "PostgreSQL"; //標明是Postgresql數據庫操作
const char* ptablename = "roadlist";//數據表名稱 table name
OGRSFDriver* pdriver = NULL;
OGRLayer* player = NULL;
OGRDataSource* pDS = NULL;
//註冊驅動，這樣ogr就知道即將打開的是什麼類型的文件
pdriver = OGRSFDriverRegistrar::GetRegistrar()->GetDriverByName(drivename);
if ( pdriver == NULL ) {
return FAILURE;
}
//驅動註冊完畢打開數據庫
pDS = pdriver->Open(filepath,0);
if ( NULL == pDS ) {
return FAILURE;
}
//打開數據庫中的數據表
player = pDS->GetLayerByName(ptablename);
if ( NULL == player ) {
return FAILURE;
}
//OGRFeature*相當於指向數據表中一條記錄的指針，根據它可以獲取每一個字段
OGRFeature* pogrfeature = NULL;
player->ResetReading();
int gid = 0;
//循環遍歷每一條記錄，這裏的遍歷是按照表中數據的存儲順序遍歷
//並不會按照主鍵唯一值順序遍歷，這和SQL的select結果的順序不一樣
//想要一樣應該創建索引，並將表數據按索引順序存儲
/*
CREATE INDEX roadlist_gid_idx
ON roadlist
USING btree
(gid);
cluster roadlist using roadlist_gid_idx;
*/
while( (pogrfeature = player->GetNextFeature()) != NULL )
{
gid++;
//獲取一條記錄中的幾何屬性字段的引用
OGRGeometry *pgeo = pogrfeature->GetGeometryRef();
if ( NULL != pgeo )
{
//判斷一下是不是自己想要的類型，這裏我的數據是道路，line數據
if ( wkbMultiLineString == pgeo->getGeometryType() || wkbLineString == pgeo->getGeometryType() )
{
OGRGeometry* pgeometry = pgeo;
//單獨處理一下multilinestring的情況
if ( wkbMultiLineString == pgeo->getGeometryType() )
{
OGRMultiLineString* pmultilinestring = (OGRMultiLineString*)pgeo;
if( 1 != pmultilinestring->getNumGeometries() )
{
return FAILURE;
}
pgeometry = pmultilinestring->getGeometryRef(0);
}
//定義OGRLineString類型指針指向幾何數據
//這樣就可以使用OGRLineString提供的函數接口了
OGRLineString* pline = (OGRLineString *)pgeometry;
int pointnum = pline->getNumPoints();
RoadRec tmp;//自定義數據類型
//使用OGRFeature類提供的 GetFieldAsInteger
//方法獲取每個字段的值，”link_id”,”road_name”都是字段名
tmp.link_id = pogrfeature->GetFieldAsInteger("link_id");
//tmp.src_id = pogrfeature->GetFieldAsInteger("src_id");
tmp.road_name = pogrfeature->GetFieldAsString("road_name");
tmp.one_way = pogrfeature->GetFieldAsInteger("one_way");
//獲得幾何屬性的每一個點座標信息
for ( int pointid = 0; pointid < pointnum;++pointid )
{
OGRPoint point;
pline->getPoint(pointid,&point);
GEO_POINT geo_point;
geo_point.x = point.getX();
geo_point.y = point.getY();
tmp.vstShplist.push_back(geo_point);
}
RoadList.push_back(tmp);
}
}
//釋放Feature資源
OGRFeature::DestroyFeature(pogrfeature);
//cout<<link_id<<endl;
}
//釋放指向該數據庫的指針
OGRDataSource::DestroyDataSource(pDS);
return SUCCESS;
}
///////////////////////////////
//使用OGR寫Postgresql
///////////////////////////////
int setFeature( const vector<RoadRec>& RoadList )
{
OGRRegisterAll();
const char* filepath =
"PG:dbname=test host=172.0.0.1 port=5432 user=postgres password=postgres";
const char* drivename = "PostgreSQL";
const char* ptablename = "roadlist";
OGRSFDriver* pdriver = NULL;
OGRLayer* player = NULL;
OGRDataSource* pDS = NULL;
pdriver = OGRSFDriverRegistrar::GetRegistrar()->GetDriverByName(drivename);
if ( pdriver == NULL ) {
return FAILURE;
}
pDS = pdriver->Open(filepath,0);
if ( NULL == pDS ) {
return FAILURE;
}
//相當於sql語句中的創建數據表，只是這裏只先指定表名稱和幾何字段屬性
player = pDS->CreateLayer( ptablename,NULL,wkbLineString,NULL );
if ( NULL == player )
{
return FAILURE;
}
//定義一個字段one_way
OGRFieldDefn* pfielddefn_oneway = new OGRFieldDefn("one_way",OFTInteger);
//在數據表中創建定義的字段
player->CreateField(pfielddefn_oneway);
OGRFieldDefn* pfielddefn_name = new OGRFieldDefn("road_name",OFTString);
player->CreateField(pfielddefn_name);
//刪除字段定義指針
delete pfielddefn_oneway;
delete pfielddefn_name;
int roadnum = RoadList.size();
//循環寫入每一條道路數據
for ( int roadcnt = 0; roadcnt < roadnum ;++roadcnt )
{
const RoadRec& roadrec = RoadList.at(roadcnt);
OGRLineString* pline = new OGRLineString;//要寫入的幾何字段
int pointnum = roadrec.vstShplist.size();
for ( int pointcnt = 0; pointcnt < pointnum ;++pointcnt )
{
const GEO_POINT& point = roadrec.vstShplist.at(pointcnt);
pline->addPoint(point.x,point.y);
}
OGRGeometry* pgeo = (OGRGeometry*)pline;
pgeo->setCoordinateDimension(2);//設置座標系維度
//創建一個指向要寫入的記錄的指針
//指定要寫入的數據庫player->GetLayerDefn()
OGRFeature* pfeature = OGRFeature::CreateFeature( player->GetLayerDefn() );
//設置當前記錄的字段值
pfeature->SetField("one_way",roadrec.one_way);
pfeature->SetField("road_name",roadrec.road_name.c_str());
if ( OGRERR_NONE != pfeature->SetGeometry( pgeo ) )
{
return FAILURE;
}
//將記錄寫入數據表
if ( OGRERR_NONE != player->CreateFeature( pfeature ) )
{
return FAILURE;
}
delete pline;
OGRFeature::DestroyFeature(pfeature);
}
OGRDataSource::DestroyDataSource(pDS);
return SUCCESS;
}
int main()
{
vector<RoadRec> roadlist;
getFeature(roadlist);
cout<<roadlist.size()<<endl;
setFeature(roadlist);
return 0;
}
編譯鏈接：g++ -o feature feature_pro.cpp -lgdal
