Read/extract pixel value of a GeoTiff

edit

Ok I finally got it working and of course, all I needed was the original GDAL Tutorial (http://www.gdal.org/gdal_tutorial.html) and some tweaking.

However, I will have to make a serious workaround to implement the opencv functionality in a regular qt window, because the highgui windows can't do what I need it to.

Here's the complete code fragment if anyone else ever needs it:

void mouseEvent(int evt, int x, int y, int flags, void* ptr)
{
    cv::Point pt(x, y);

    if (evt == CV_EVENT_LBUTTONDOWN)
    {
        Point*p = (Point*)ptr;
        p->x = x;
        p->y = y;
        cout<<*p;

        GDALAllRegister();
        GDALDatasetH hDataset = GDALOpen( "C:/path/to/project/image.tif", GA_ReadOnly );
        if( hDataset == NULL )
        {
            qDebug() << "data set is null";
        }

        GDALRasterBandH hBand;
        int             nBlockXSize, nBlockYSize;
        int             bGotMin, bGotMax;
        double          adfMinMax[2];

        hBand = GDALGetRasterBand( hDataset, 1 );
        GDALGetBlockSize( hBand, &nBlockXSize, &nBlockYSize );

        adfMinMax[0] = GDALGetRasterMinimum( hBand, &bGotMin );
        adfMinMax[1] = GDALGetRasterMaximum( hBand, &bGotMax );
        if( ! (bGotMin && bGotMax) )
            GDALComputeRasterMinMax( hBand, TRUE, adfMinMax );

        float *pafScanline;
        int   nXSize = GDALGetRasterBandXSize( hBand );
        pafScanline = (float *) CPLMalloc(sizeof(float)*nXSize);
        GDALRasterIO( hBand, GF_Read, x, y, 1, 1,
                      pafScanline, nXSize, 1, GDT_Float32,
                      0, 0 );

        qDebug() << x << y << pafScanline[0];

    }

}