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& 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;

//注冊驅動，這樣ogr就知道即將打開的是什么類型的文件

pdriver = OGRSFDriverRegistrar::GetRegistrar()->GetDriverByName(drivename);

if ( pdriver == NULL ) {

return FAILURE;

}

//驅動注冊完畢打開數據庫

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*相當于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，這里的遍歷是按照表中數據的存儲順序遍歷

//并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，并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，這里我的數據是道路，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坐標信息

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<

}

//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& 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;

}

//相當于sql語句中的創建數據表，只是這里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);//設置坐標系維度

//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 roadlist;

getFeature(roadlist);

cout<

setFeature(roadlist);

return 0;

}

編譯鏈接：g++ -o feature feature_pro.cpp -lgdal

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