GDAL 是一個很強大的可以讀取很多格式 的帶有GIS資訊的柵格型影象。前陣子專案中需要讀取遙感影象，並顯示到QT介面，由於遙感影象一般很大，所以採取新開一個讀圖執行緒的方式來讀取，防止介面假死。下面是程式碼共享，測試通過讀取500MB的24000*24000畫素GeoTiff圖並在QT的QGraphicsView中顯示。

環境：VS2005+SP1, Qt 4.6.0, GDAL 1.6.2

檔案：commontoolfunctions.h, gdalimagereaderthread.h, gdalimagereaderthread.cpp

commontoolfunctions.h檔案如下：

/* * 工具函式：網上找來的根據兩點的經緯度座標計算兩個點的大地距離。 */ #ifndef COMMONTOOLFUNCTIONS_H #define COMMONTOOLFUNCTIONS_H #include <math.h> #define EARTH_RADIUS 6378.137 #define MY_PI 3.14159265358979 #define LB_CONVERT_TO_RAD(d) (d * MY_PI / 180.0) /* * 輸入經緯度座標，單位'度'。 * 返回值單位為公里。 * code from google maps. 近似值. */ double CalcDistanceByLB(double lat1, double lng1, double lat2, double lng2) { double radLat1 = LB_CONVERT_TO_RAD(lat1); double radLat2 = LB_CONVERT_TO_RAD(lat2); double a = radLat1 - radLat2; double b = LB_CONVERT_TO_RAD(lng1) - LB_CONVERT_TO_RAD(lng2); double s = 2 * asin(sqrt(pow(sin(a/2),2) + cos(radLat1)*cos(radLat2)*pow(sin(b/2),2))); s = s * EARTH_RADIUS; return s; } #endif

gdalimagereaderthread.h檔案如下：

/* * QT執行緒類：使用GDAL讀取影象檔案並轉為QImage的執行緒。 * 建立：MulinB * 日期：2010-1-8 * 上次修改: 2010-06-20 * HUST-IPRAI-CVL */ #ifndef GDALIMAGEREADERTHREAD_H #define GDALIMAGEREADERTHREAD_H #include <QThread> #include <gdal_priv.h> //for GDAL class QImage; class RSI_MapCanvas; class RSI_ImageReaderThread : public QThread { Q_OBJECT public: RSI_ImageReaderThread(RSI_MapCanvas* pCanvas); ~RSI_ImageReaderThread(); public: void ReadFile(const QString& imageFileName); //使用該函式讀取檔案 protected: void run(); //執行緒函式 private: RSI_MapCanvas* m_pCanvas; QString m_imageFileName; private: //GDAL讀取影象檔案時的臨時變數 GDALRasterBand* m_pBand_GDAL_; int m_nXSize_GDAL_; int m_nYSize_GDAL_; void* m_pDataBufStart_GDAL_; int m_nBufXSize_GDAL_; int m_nBufYSize_GDAL_; GDALDataType m_eBufDataType_GDAL_; int m_nBufPixSpace_GDAL_; int m_nBufLineSpace_GDAL_; private: enum IMG_OPEN_DRIVER_T { RSI_IMG_DRIVER_UNDEF = 0, //未定義的開啟方式 RSI_USE_OPENCV, //使用opencv RSI_USE_GDAL, //使用GDAL }; private: //將影象寬度位元組數32位對齊 inline int Get32bitAlignedWidthBytes(int nImgPixWidth, int nBytesPerPix); //GDAL buffer 轉 QImage QImage* CvtGDALBufferToGrayQImage(uchar* &pafScanblock, int nImgSizeX, int nImgSizeY, GDALDataType pixType); //將非8位的灰度圖轉換為8位灰度圖 template <class T> void CvtImgDataTo8bitGrayImg(T* pOrigData, int nImgSizeX, int nImgSizeXAligned32bit, int nImgSizeY, uchar* pNew8bitImgBuf, int nNewImgSizeXAligned32bit, T maxVal, T minVal); }; #endif // GDALIMAGEREADERTHREAD_H

gdalimagereaderthread.cpp檔案如下：

/* * QT執行緒類：使用GDAL讀取影象檔案並轉為QImage的執行緒。 * 建立：MulinB * 日期：2010-1-8 * 上次修改: 2010-06-20 * TODO: 1.影象解析度轉換計算貌似有問題... 2.程式碼比較亂，沒時間整理...囧... * HUST-IPRAI-CVL */ #include "GDALImageReaderThread.h" #include "iplimagetoqimage.h" //for IplImage converting to QImage #include "commontoolfunctions.h" //for calculate distance by LB #include <cv.h> //for OpenCV #include <highgui.h> //for OpenCV #include <limits.h> //for INT_MAX, INT_MIN, ... #include <float.h> //for FLT_MAX, FLT_MIN, ... QMutex G_imageReadMutex; QWaitCondition G_imageReadComplete; RSI_ImageReaderThread::RSI_ImageReaderThread(RSI_MapCanvas* pCanvas) : m_pCanvas(pCanvas) { } RSI_ImageReaderThread::~RSI_ImageReaderThread() { } //執行緒函式 void RSI_ImageReaderThread::run() { //這裡只將GDAL最費時的RasterIO()函式作為新執行緒 /* GDALRasterBand::RasterIO() parameters: eRWFlag Either GF_Read to read a region of data, or GT_Write to write a region of data. nXOff The pixel offset to the top left corner of the region of the band to be accessed. This would be zero to start from the left side. nYOff The line offset to the top left corner of the region of the band to be accessed. This would be zero to start from the top. nXSize The width of the region of the band to be accessed in pixels. nYSize The height of the region of the band to be accessed in lines. pData The buffer into which the data should be read, or from which it should be written. This buffer must contain at least nBufXSize * nBufYSize words of type eBufType. It is organized in left to right, top to bottom pixel order. Spacing is controlled by the nPixelSpace, and nLineSpace parameters. nBufXSize the width of the buffer image into which the desired region is to be read, or from which it is to be written. nBufYSize the height of the buffer image into which the desired region is to be read, or from which it is to be written. eBufType the type of the pixel values in the pData data buffer. The pixel values will automatically be translated to/from the GDALRasterBand data type as needed. nPixelSpace The byte offset from the start of one pixel value in pData to the start of the next pixel value within a scanline. If defaulted (0) the size of the datatype eBufType is used. nLineSpace The byte offset from the start of one scanline in pData to the start of the next. If defaulted the size of the datatype eBufType * nBufXSize is used. */ G_imageReadMutex.lock(); m_pBand_GDAL_->RasterIO(GF_Read, 0, 0, m_nXSize_GDAL_, m_nYSize_GDAL_, m_pDataBufStart_GDAL_, m_nBufXSize_GDAL_, m_nBufYSize_GDAL_, m_eBufDataType_GDAL_, m_nBufPixSpace_GDAL_, m_nBufLineSpace_GDAL_); //G_imageReadComplete.wakeAll(); G_imageReadMutex.unlock(); } //讀圖函式：使用GDAL和OpenCV讀取影象檔案 void RSI_ImageReaderThread::ReadFile(const QString& imageFileName) { m_imageFileName = imageFileName; if (m_imageFileName.isEmpty() || m_pCanvas == NULL) return; //選擇開啟影象的驅動方式: GDAL or OpenCV const QString strOpenCV = tr("OpenCV"); const QString strGDAL = tr("GDAL"); IMG_OPEN_DRIVER_T eOpenDriverType; QStringList items; //for input dialog items << strOpenCV << strGDAL; int curDriverItemIdx = 0; //先根據副檔名推薦開啟方式 QString fileExtName = m_imageFileName.right(3).toLower(); if (fileExtName == QString("bmp") || fileExtName == QString("png") || fileExtName == QString("jpg") || fileExtName == QString("peg") || fileExtName == QString("jpe") || fileExtName == QString("ppm") || fileExtName == QString("pbm") || fileExtName == QString("pgm")) { //如果是常用格式，推薦使用OpenCV開啟: (*.bmp *.png *.jpg *.jpeg *.jpe *.ppm *.pgm *.pbm) eOpenDriverType = RSI_USE_OPENCV; //根據副檔名來推薦使用哪種開啟方式 curDriverItemIdx = 0; } else { eOpenDriverType = RSI_USE_GDAL; curDriverItemIdx = 1; } //彈出對話方塊讓使用者選擇使用哪種驅動方式開啟影象 bool dlgOk; QString itemSel = QInputDialog::getItem(m_pCanvas, tr("Please select..."), tr("Driver for image opener:"), items, curDriverItemIdx, false, &dlgOk); if (dlgOk && !itemSel.isEmpty()) { if (itemSel == strOpenCV) { eOpenDriverType = RSI_USE_OPENCV; } else if (itemSel == strGDAL) { eOpenDriverType = RSI_USE_GDAL; } } else { return; } //進度條 int progressBarValue = 2; QProgressDialog progress(tr("Reading image file..."), tr("Abort"), 0, 100, m_pCanvas); QProgressBar prgBar(&progress); prgBar.setTextVisible(false); //不顯示百分比 progress.setBar(&prgBar); progress.setWindowModality(Qt::ApplicationModal); progress.setCancelButton(NULL); progress.setWindowTitle(tr("Please wait...")); // 標題 progress.setValue(progressBarValue); //use GDAL and OpenCV open image files if (eOpenDriverType == RSI_USE_OPENCV) { //開啟影象檔案 IplImage* pIplImg = NULL; //宣告IplImage指標 if ((pIplImg = cvLoadImage(m_imageFileName.toStdString().c_str(), 1)) == 0) //使用OpenCV highgui開啟影象檔案 { QMessageBox::warning(m_pCanvas, tr("Failed"), tr("Open Image File Failed!"), tr("OK")); return; } //讀取影象資訊 QString rsiFileInfo; //影象資訊 QString tempStr; tempStr = tr("Size is %1 x %2 x [%3(bits) x %4(channels)]/n") .arg(pIplImg->width) .arg(pIplImg->height) .arg(pIplImg->depth) .arg(pIplImg->nChannels); rsiFileInfo += tempStr; //顯示 uchar* imageDataBuffer = NULL; QImage* pQImage = IplImageToQImage(pIplImg, &imageDataBuffer); //轉換成QImage //建立圖層 RSI_ImageLayer* pImageLayer = new RSI_ImageLayer(*pQImage); pImageLayer->setLayerName(m_imageFileName); pImageLayer->setImageLayerInfo(rsiFileInfo); pImageLayer->setBufferToBeFree(imageDataBuffer); //記錄到m_bufferToBeFree中，待關閉影象時釋放buffer記憶體 pImageLayer->setVisible(false); //預設不顯示 pImageLayer->setFlag(QGraphicsItem::ItemIsMovable, false); m_pCanvas->AddImageLayer(pImageLayer); //釋放臨時記憶體 cvReleaseImage(&pIplImg); delete pQImage; goto _READ_IMAGE_FILE_OVER; //讀取完畢直接返回 } else if (eOpenDriverType == RSI_USE_GDAL) { //如果是遙感影象格式，則使用GDAL開啟 GDALAllRegister(); GDALDataset* poDataset; //GDAL資料集 poDataset = (GDALDataset*)GDALOpen(m_imageFileName.toStdString().c_str(), GA_ReadOnly); if( poDataset == NULL ) { //QMessageBox::warning(NULL, tr("Failed"), tr("GDAL Open Image File Failed!"), tr("OK")); return; } //讀取遙感影象資訊 QString rsiFileInfo; //遙感影象資訊 QString tempStr; tempStr = tr("GDAL Driver: %1/%2/n") .arg(QString(poDataset->GetDriver()->GetDescription())) .arg(QString(poDataset->GetDriver()->GetMetadataItem(GDAL_DMD_LONGNAME))); rsiFileInfo += tempStr; tempStr = tr("Size is %1 x %2 x %3(bands)/n") .arg(poDataset->GetRasterXSize()) .arg(poDataset->GetRasterYSize()) .arg(poDataset->GetRasterCount()); rsiFileInfo += tempStr; /* 地理參考座標系統: The returned string defines the projection coordinate system of the image in OpenGIS WKT format. */ double adfGeoTransform[6]; QString prjRefStr(poDataset->GetProjectionRef()); if (prjRefStr.isEmpty()) { prjRefStr = tr("none"); //如果此欄位為空，那麼投影方式可能是GCPs } else //非空時才讀取仿射變換資訊 { tempStr = tr("Projection(WKT format) is '%1'/n").arg(prjRefStr); rsiFileInfo += tempStr; //非空時才讀取仿射變換資訊 /* 仿射地理變換資訊： adfGeoTransform[0] // top left x adfGeoTransform[1] // w-e pixel resolution adfGeoTransform[2] // rotation, 0 if image is "north up" adfGeoTransform[3] // top left y adfGeoTransform[4] // rotation, 0 if image is "north up" adfGeoTransform[5] // n-s pixel resolution 計算某一點的地理座標可以如下計算： Xgeo = GT(0) + Xpixel*GT(1) + Yline*GT(2) Ygeo = GT(3) + Xpixel*GT(4) + Yline*GT(5) */ poDataset->GetGeoTransform( adfGeoTransform ); tempStr = tr("Origin Cords = (%1,%2)/n") .arg(adfGeoTransform[0], 0, 'f', 6) .arg(adfGeoTransform[3], 0, 'f', 6); rsiFileInfo += tempStr; tempStr = tr("Pixel Size(degrees) = (%1,%2)/n") .arg(adfGeoTransform[1], 0, 'f', 6) .arg(adfGeoTransform[5], 0, 'f', 6); rsiFileInfo += tempStr; } //讀取GCPs投影方式 QString prjGCPStr(poDataset->GetGCPProjection()); if (prjGCPStr.isEmpty()) { prjGCPStr = tr("none"); } else { tempStr = tr("GCPs Prj is '%1'/n").arg(prjGCPStr); rsiFileInfo += tempStr; int nGCPs = poDataset->GetGCPCount(); //獲得GCP控制點的個數 const GDAL_GCP* pGCPs = poDataset->GetGCPs(); //獲得GCP控制點 tempStr = tr("Number of GCPs: %1/n").arg(nGCPs); rsiFileInfo += tempStr; //由GCPs獲得仿射變換引數 GDALGCPsToGeoTransform( nGCPs, pGCPs, adfGeoTransform, TRUE ); tempStr = tr("Origin Cords = (%1,%2)/n") .arg(adfGeoTransform[0], 0, 'f', 6) .arg(adfGeoTransform[3], 0, 'f', 6); rsiFileInfo += tempStr; tempStr = tr("Pixel Size(degrees) = (%1,%2)/n") .arg(adfGeoTransform[1], 0, 'f', 6) .arg(adfGeoTransform[5], 0, 'f', 6); rsiFileInfo += tempStr; } //根據adfGeoTransform計算每個畫素代表多少米距離 double oriCordL = adfGeoTransform[0]; double oriCordB = adfGeoTransform[3]; double tempL, tempB; GDALApplyGeoTransform(adfGeoTransform, 100, 0, &tempL, &tempB); //計算(100,0)畫素處的L,B座標 double tempDist = CalcDistanceByLB(oriCordL, oriCordB, tempL, tempB); double xMeterPerPix = tempDist * 1000.0 / 100.0; //單位為米 GDALApplyGeoTransform(adfGeoTransform, 0, 100, &tempL, &tempB); //計算(0,100)畫素處的L,B座標 tempDist = CalcDistanceByLB(oriCordL, oriCordB, tempL, tempB); double yMeterPerPix = tempDist * 1000.0 / 100.0; //單位為米 tempStr = tr("Pixel Size(meters) = (%1,%2)/n") .arg(xMeterPerPix, 0, 'f', 6) .arg(yMeterPerPix, 0, 'f', 6); rsiFileInfo += tempStr; //讀取影象大小 int nBandCount = poDataset->GetRasterCount(); int nImgSizeX = poDataset->GetRasterXSize(); int nImgSizeY = poDataset->GetRasterYSize(); //讀取影象資料點型別 GDALRasterBand* preBand = poDataset->GetRasterBand(1); //預讀取遙感的第一個波段 GDALDataType prePixType = preBand->GetRasterDataType(); int prePixSize = GDALGetDataTypeSize(prePixType) / 8; //GDALGetDataTypeSize得到的是bit if (nBandCount >= 3 && prePixSize == 1) //多於3個波段的影象給使用者選擇是否合併前三個波段用RGB顯示 { //QMessageBox::StandardButton userAnswer = QMessageBox::Yes; QMessageBox::StandardButton userAnswer = QMessageBox::question(m_pCanvas, tr("Choose image show format"), tr("%1 bands detected!/nWill you show it in RGB color format using the first three bands?").arg(nBandCount), QMessageBox::Yes|QMessageBox::No); if (userAnswer == QMessageBox::Yes) { //--------將前三個波段組合成RGB顏色顯示, 使用QImage::Format_RGB32格式顯示--------- uchar* pafScanblock = (uchar*)malloc(4*(nImgSizeX)*(nImgSizeY)); //Format_RGB32每個畫素4個位元組: RGBA //assert(pafScanblock != NULL); if (pafScanblock == NULL) { QMessageBox::warning(m_pCanvas, tr("Failed"), tr("Open Image File Failed! Out of memory!"), tr("OK")); delete poDataset; //關閉資料集 goto _READ_IMAGE_FILE_OVER; } memset(pafScanblock, 0x00, 4*(nImgSizeX)*(nImgSizeY)); //讀取影象 for (int nB=0; nB<nBandCount; nB++) { GDALRasterBand* poBand = poDataset->GetRasterBand(nB+1); //遙感的一個波段 assert(poBand != NULL); GDALDataType pixType = poBand->GetRasterDataType(); int pixSize = GDALGetDataTypeSize(pixType) / 8; //GDALGetDataTypeSize得到的是bit assert(pixSize == 1); //彩色圖的每個通道的size應該是1個位元組 //用RasterIO()讀取影象資料 //poBand->RasterIO(GF_Read, 0, 0, nImgSizeX, nImgSizeY, // pafScanblock+nB, nImgSizeX, nImgSizeY, pixType, 4, 0); G_imageReadMutex.lock(); m_pBand_GDAL_ = poBand; m_nXSize_GDAL_ = nImgSizeX; m_nYSize_GDAL_ = nImgSizeY; m_pDataBufStart_GDAL_ = pafScanblock+nB; //注意！ m_nBufXSize_GDAL_ = nImgSizeX; m_nBufYSize_GDAL_ = nImgSizeY; m_eBufDataType_GDAL_ = pixType; m_nBufPixSpace_GDAL_ = 4; //注意！ m_nBufLineSpace_GDAL_ = 0; start(); //開始新執行緒 G_imageReadMutex.unlock(); while (this->isRunning()) { progressBarValue += 8; progress.setValue(progressBarValue % 100); QThread::msleep(1000); //注意：這裡是讓主執行緒sleep，而不是新執行緒 } //G_imageReadComplete.wait(&G_imageReadMutex); //progressBarValue += 20; //progress.setValue(progressBarValue % 100); //G_imageReadMutex.unlock(); } //組合成彩色QImage QImage* pQImage = NULL; pQImage = new QImage(pafScanblock, nImgSizeX, nImgSizeY, QImage::Format_RGB32); //注意：QImage: each scanline of data in the image must also be 32-bit aligned //assert(pQImage != NULL); if (pQImage == NULL) { QMessageBox::warning(m_pCanvas, tr("Failed"), tr("Open Image File Failed! Out of memory!"), tr("OK")); free(pafScanblock); delete poDataset; //關閉資料集 goto _READ_IMAGE_FILE_OVER; } //建立圖層 RSI_ImageLayer* pImageLayer = new RSI_ImageLayer(*pQImage); if (pImageLayer == NULL) { QMessageBox::warning(m_pCanvas, tr("Failed"), tr("Open Image File Failed! Out of memory!"), tr("OK")); free(pafScanblock); delete pQImage; delete poDataset; //關閉資料集 goto _READ_IMAGE_FILE_OVER; } pImageLayer->setLayerName(tr("3 bands composited color image") + QString("(") + m_imageFileName + QString(")")); pImageLayer->setImageLayerInfo(rsiFileInfo); pImageLayer->setGeoTransform(adfGeoTransform); pImageLayer->setResolutionX(xMeterPerPix); pImageLayer->setResolutionY(yMeterPerPix); pImageLayer->setBufferToBeFree(pafScanblock); //記錄到m_bufferToBeFree中，待關閉影象時釋放buffer記憶體 pImageLayer->setVisible(false); //預設不顯示 pImageLayer->setFlag(QGraphicsItem::ItemIsMovable, false); m_pCanvas->AddImageLayer(pImageLayer); //釋放臨時物件 delete pQImage; delete poDataset; //關閉資料集 goto _READ_IMAGE_FILE_OVER; //讀取完畢直接返回 } } //------------按照波段分別讀取，每個波段顯示成一個灰度圖------------- //讀取影象 for (int nB=0; nB<nBandCount; nB++) { GDALRasterBand* poBand = poDataset->GetRasterBand(nB+1); //遙感的一個波段 assert(poBand != NULL); GDALDataType pixType = poBand->GetRasterDataType(); int pixSize = GDALGetDataTypeSize(pixType) / 8; //GDALGetDataTypeSize得到的是bit //注意：QImage: each scanline of data in the image must also be 32-bit aligned int nImgSizeXAligned32bit = Get32bitAlignedWidthBytes(nImgSizeX, pixSize) / pixSize; //對齊後的畫素寬度 uchar* pafScanblock = (uchar*)malloc(pixSize*(nImgSizeXAligned32bit)*(nImgSizeY)); //assert(pafScanblock != NULL); if (pafScanblock == NULL) { QMessageBox::warning(m_pCanvas, tr("Failed"), tr("Open Image File Failed! Out of memory!"), tr("OK")); delete poDataset; //關閉資料集 goto _READ_IMAGE_FILE_OVER; } //用RasterIO()讀取影象資料 //poBand->RasterIO(GF_Read, 0, 0, nImgSizeX, nImgSizeY, // pafScanblock, nImgSizeXAligned32bit, nImgSizeY, pixType, 0, 0); G_imageReadMutex.lock(); m_pBand_GDAL_ = poBand; m_nXSize_GDAL_ = nImgSizeX; m_nYSize_GDAL_ = nImgSizeY; m_pDataBufStart_GDAL_ = pafScanblock; m_nBufXSize_GDAL_ = nImgSizeXAligned32bit; m_nBufYSize_GDAL_ = nImgSizeY; m_eBufDataType_GDAL_ = pixType; m_nBufPixSpace_GDAL_ = 0; m_nBufLineSpace_GDAL_ = 0; start(); //開始新執行緒 G_imageReadMutex.unlock(); while (this->isRunning()) { progressBarValue += 8; progress.setValue(progressBarValue % 100); QThread::msleep(1000); //注意：這裡是讓主執行緒sleep，而不是新執行緒 } //G_imageReadComplete.wait(&G_imageReadMutex); //progressBarValue += 20; //progress.setValue(progressBarValue % 100); //G_imageReadMutex.unlock(); //轉化為QImage QImage* pQImage = CvtGDALBufferToGrayQImage(pafScanblock, nImgSizeX, nImgSizeY, pixType); if (pQImage == NULL) { QMessageBox::warning(m_pCanvas, tr("Failed"), tr("Open Image File Failed! Out of memory!"), tr("OK")); free(pafScanblock); delete poDataset; //關閉資料集 goto _READ_IMAGE_FILE_OVER; } //建立圖層 RSI_ImageLayer* pImageLayer = new RSI_ImageLayer(*pQImage); if (pImageLayer == NULL) { QMessageBox::warning(m_pCanvas, tr("Failed"), tr("Open Image File Failed! Out of memory!"), tr("OK")); free(pafScanblock); delete pQImage; delete poDataset; //關閉資料集 goto _READ_IMAGE_FILE_OVER; } pImageLayer->setLayerName(tr("band") + QString("%1").arg(nB+1) + tr(": pixel type = ") + QString(GDALGetDataTypeName(pixType)) + QString("(") + QString("%1").arg(pixSize) + tr(" bytes)")); pImageLayer->setImageLayerInfo(rsiFileInfo); pImageLayer->setGeoTransform(adfGeoTransform); pImageLayer->setResolutionX(xMeterPerPix); pImageLayer->setResolutionY(yMeterPerPix); pImageLayer->setBufferToBeFree(pafScanblock); //記錄到m_bufferToBeFree中，待關閉影象時釋放buffer記憶體 pImageLayer->setVisible(false); //預設不顯示 pImageLayer->setFlag(QGraphicsItem::ItemIsMovable, false); m_pCanvas->AddImageLayer(pImageLayer); //釋放臨時物件 delete pQImage; } delete poDataset; //關閉資料集 goto _READ_IMAGE_FILE_OVER; //讀取完畢直接返回 } //end if eOpenDriverType _READ_IMAGE_FILE_OVER: return; } //將影象寬度位元組數32位對齊，返回對齊後的位元組數 int RSI_ImageReaderThread::Get32bitAlignedWidthBytes(int nImgPixWidth, int nBytesPerPix) { return ((nImgPixWidth*nBytesPerPix/4) + (((nImgPixWidth*nBytesPerPix)%4)==0 ? 0 : 1)) * 4; } //GDAL buffer 轉 QImage QImage* RSI_ImageReaderThread::CvtGDALBufferToGrayQImage(uchar* &pafScanblock, int nImgSizeX, int nImgSizeY, GDALDataType pixType) { //準備顏色表 QVector<QRgb> vcolorTable; for (int i = 0; i < 256; i++) { vcolorTable.push_back(qRgb(i, i, i)); } int pixSize = GDALGetDataTypeSize(pixType) / 8; int nImgSizeXAligned32bit = Get32bitAlignedWidthBytes(nImgSizeX, pixSize) / pixSize; //對齊後的畫素寬度 int nNewImgSizeXAligned32bit = Get32bitAlignedWidthBytes(nImgSizeX, 1); //根據pixType轉換 if (pixType == GDT_Byte) { //do nothing } else //add by baolc, 2010-06-10 { //將16位資料轉為8位灰度顯示 uchar* pNew_pafScanblock_8bit = (uchar*)malloc(nNewImgSizeXAligned32bit * nImgSizeY); if (pNew_pafScanblock_8bit == NULL) { QMessageBox::warning(m_pCanvas, tr("Failed"), tr("Open Image File Failed! Out of memory!"), tr("OK")); return NULL; } if (pixType == GDT_UInt16) { CvtImgDataTo8bitGrayImg<ushort>((ushort*)pafScanblock, nImgSizeX, nImgSizeXAligned32bit, nImgSizeY, pNew_pafScanblock_8bit, nNewImgSizeXAligned32bit, USHRT_MAX, 0); } else if (pixType == GDT_Int16) { CvtImgDataTo8bitGrayImg<short>((short*)pafScanblock, nImgSizeX, nImgSizeXAligned32bit, nImgSizeY, pNew_pafScanblock_8bit, nNewImgSizeXAligned32bit, SHRT_MAX, SHRT_MIN); } else if (pixType == GDT_UInt32) { CvtImgDataTo8bitGrayImg<int>((int*)pafScanblock, nImgSizeX, nImgSizeXAligned32bit, nImgSizeY, pNew_pafScanblock_8bit, nNewImgSizeXAligned32bit, UINT_MAX, 0); } else if (pixType == GDT_Int32) { CvtImgDataTo8bitGrayImg<unsigned int>((unsigned int*)pafScanblock, nImgSizeX, nImgSizeXAligned32bit, nImgSizeY, pNew_pafScanblock_8bit, nNewImgSizeXAligned32bit, INT_MAX, INT_MIN); } else if (pixType == GDT_Float32) { CvtImgDataTo8bitGrayImg<float>((float*)pafScanblock, nImgSizeX, nImgSizeXAligned32bit, nImgSizeY, pNew_pafScanblock_8bit, nNewImgSizeXAligned32bit, FLT_MAX, FLT_MIN); } else if (pixType == GDT_Float64) { CvtImgDataTo8bitGrayImg<double>((double*)pafScanblock, nImgSizeX, nImgSizeXAligned32bit, nImgSizeY, pNew_pafScanblock_8bit, nNewImgSizeXAligned32bit, DBL_MAX, DBL_MIN); } free(pafScanblock); //釋放原來的記憶體 pafScanblock = pNew_pafScanblock_8bit; //指向新記憶體，注意，因為引數傳進來是引用，所以可以改變其指向 } QImage* pQImage = new QImage(pafScanblock, nImgSizeX, nImgSizeY, QImage::Format_Indexed8); //注意：QImage: each scanline of data in the image must also be 32-bit aligned if (pQImage == NULL) { QMessageBox::warning(m_pCanvas, tr("Failed"), tr("Open Image File Failed! Out of memory!"), tr("OK")); } else { pQImage->setColorTable(vcolorTable); } return pQImage; } //將非8位的灰度圖轉換為8位灰度圖 template <class T> void RSI_ImageReaderThread::CvtImgDataTo8bitGrayImg(T* pOrigData, int nImgSizeX, int nImgSizeXAligned32bit, int nImgSizeY, uchar* pNew8bitImgBuf, int nNewImgSizeXAligned32bit, T maxVal, T minVal) { int oldIdxPos = 0; int newIdxPos = 0; T minPixVal = maxVal; T maxPixVal = minVal; T curPixVal; //找到最大值和最小值 for (int niY=0; niY<nImgSizeY; niY++) { for (int niX=0; niX<nImgSizeX; niX++) { oldIdxPos = niY * nImgSizeXAligned32bit + niX; curPixVal = pOrigData[oldIdxPos]; if (curPixVal > maxPixVal) maxPixVal = curPixVal; if (curPixVal < minPixVal) minPixVal = curPixVal; } } //根據最大值最小值進行歸一化 double pixValRange = maxPixVal - minPixVal; if (pixValRange == 0) pixValRange = 1; for (int niY=0; niY<nImgSizeY; niY++) { for (int niX=0; niX<nImgSizeX; niX++) { oldIdxPos = niY * nImgSizeXAligned32bit + niX; newIdxPos = niY * nNewImgSizeXAligned32bit + niX; curPixVal = pOrigData[oldIdxPos]; pNew8bitImgBuf[newIdxPos] = (uchar)((curPixVal - minPixVal) / pixValRange * 255); } } }

在我的機器上讀取的一張遙感影象裡，將上面讀取到的imgFileInfo經過翻譯後顯示出來如下所示：

GDAL Driver: GTiff/GeoTIFF 影象大小: 24000 X 24000 X 1(波段) GCPs投影方式: GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.2572235630016,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORITY["EPSG","4326"]] GCP個數: 4 影象左上角座標: (116.906446, 36.204771) 畫素跨度(經緯度): (0.000031, -0.000022) 畫素跨度(米): (3.486195, 1.279424)