Copied the red band of the RGB TIFF file with GDAL in C++

Question

I'm a rookie in GDAL and C++. I tried to copy the red band of the RGB tif file with Create() and GetRasterBand(1)->RasterIO(). I got the right size of my new tif file, but all the value of the new image is 128. I tried to check the value while it run, and I'm sure they have the same value in the red band of the RGB TIFF file. I guessed there is something wrong in the GetRasterBand(1)->RasterIO(). However, I still have no idea after checking the document.

This project need to run with the Visual Studio 2008 on Win10, so I used the version 2.2.3 of GDAL.

#include "stdafx.h"
#include "stdio.h"
#include "gdal.h"
#include "gdal_priv.h"
#include "cpl_conv.h" //for CPLMalloc()
#include <iostream>
using namespace std;

int _tmain(int argc, _TCHAR* argv[]) {
//Register GDAL
 GDALAllRegister();

//image file input_file
const char* input = "C:\\Users\\GOLiF\\Documents\\Visual Studio 2008\\Projects\\GDAL_223\\GDAL_223\\94212060_20190924_109EMAP.tif";
const char* output = "C:\\Users\\GOLiF\\Documents\\Visual Studio 2008\\Projects\\GDAL_223\\GDAL_223\\test.tif";

GDALDataset *pOldDS, *pNewDS ;
GDALDriver *pDriverTiff ;
int nRows, nCols ;
double transform[6] ;
double noData ;

pOldDS = (GDALDataset*) GDALOpen( input, GA_ReadOnly ) ;

nRows = pOldDS ->GetRasterBand(1) ->GetYSize() ;
nCols = pOldDS ->GetRasterBand(1) ->GetXSize() ;
noData = pOldDS ->GetRasterBand(1) ->GetNoDataValue() ;
pOldDS ->GetGeoTransform(transform) ;

pDriverTiff = GetGDALDriverManager()->GetDriverByName("GTiff") ;

pNewDS =  pDriverTiff->Create( output, nCols, nRows, 1, GDT_Int16, NULL) ;
pNewDS->SetGeoTransform(transform) ;
pNewDS->GetRasterBand(1)->SetNoDataValue(noData) ;

short *oldRow = (short *) CPLMalloc(sizeof(short)*nCols) ;
short *newRow = (short *) CPLMalloc(sizeof(short)*nCols) ;

for (int i = 0 ; i < nRows ; i++){
    pOldDS->GetRasterBand(1)->RasterIO(GF_Read, 0, i, nCols, 1, oldRow, nCols, 1, GDT_Int16, 0, 0) ;
    for (int j = 0 ; j < nCols ; j++){
        if (oldRow[j] == noData ){
            newRow[j] = noData ;
            //cout << "nodata : newrow[" << j << "] = " << newrow[j] << endl;
            //system("pause");
        }
        else{
            newRow[j] = oldRow[j] ;
            //cout << "oldrow[" << j << " ]= " << oldRow[j] << endl;
            //cout << "newrow[" << j << " ]= " << newRow[j] << endl;
            //system("pause");
        }
    }
    pNewDS->GetRasterBand(1)->RasterIO(GF_Write, 0, i, nCols, 1, newRow, nCols, 1, GDT_Int16, 0, 0) ;
    //cout << "newrow= " << &newRow << endl;
}

GDALClose(pOldDS);
GDALClose(pNewDS);

system("pause");

}

Answer 1

I just remembered that I had this problem also many years ago, it's in your close statements:

GDALClose(pOldDS);
GDALClose(pNewDS);

From the help document

Equivalent of the C callable GDALClose(). Except that GDALClose() first decrements the reference count, and then closes only if it has dropped to zero. For Windows users, it is not recommended to use the delete operator on the dataset object because of known issues when allocating and freeing memory across module boundaries. Calling GDALClose() is then a better option.

Which means delete pOldDS; isn't a safe option so the best way is with GDALClose. However the C callable GDALClose (GDALDatasetH hDS) expects a parameter of type GDALDatasetH, which is different to GDALDataset*, so when I changed my close statements to cast the pointer to a handle e.g. GDALClose((GDALDatasetH)FirstClass_DS); the dataset was closed properly and flushed to disc. Can you try changing your close statements to:

pNewDS->FlushCache(); // only need to flush the dataset that has been written to
GDALClose((GDALDatasetH)pOldDS);
GDALClose((GDALDatasetH)pNewDS);
GDALDestroyDriverManager(); // this should remove any remaining locks but no more GDAL functions from here will work

and see if that fixes the problem.