<HTML dir=ltr><HEAD><TITLE>Re: [gdal-dev] General Questions about gdal usage with Grib1 Data Set</TITLE>
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<DIV dir=ltr><FONT size=2>Hi All,</FONT></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr><FONT size=2>I have an oddity when trying to read a grib1 dataset.</FONT></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr><FONT size=2>When I extract the data using code:</FONT></DIV>
<DIV dir=ltr><FONT size=2></FONT> </DIV>
<DIV dir=ltr> hBand = GDALGetRasterBand(hSrcDS, 1 );</DIV>
<DIV dir=ltr> float *pafScanline;<BR> int nXSize = GDALGetRasterBandXSize( hBand );</DIV>
<DIV dir=ltr> pafScanline = (float *) CPLMalloc(sizeof(float)*nXSize);<BR> GDALRasterIO( hBand, GF_Read, 0, 0, nXSize, 1,<BR> pafScanline, nXSize, 1, GDT_Float32,<BR> 0, 0 );</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr> for( int j = 0; j < nXSize; j++ )<BR> std::cout << pafScanline[j] << std::endl;</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>I am seeing values that are along the lines of:</DIV>
<DIV dir=ltr>12.86<BR>12.802<BR>12.734<BR>12.671<BR>12.562<BR>12.425<BR>12.241<BR>12.12<BR>12.043<BR>12.035<BR>11.986<BR>11.917<BR>11.83<BR>11.776</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>The same grib1 file when dumped using wgrib produces values ( degrees Kelvin ):</DIV>
<DIV dir=ltr>295.552<BR>295.565<BR>295.577<BR>295.589<BR>295.6<BR>295.61<BR>295.619<BR>295.626<BR>295.633<BR>295.639</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>As an additional piece of information when I use the same above code and extract values that are less that 1 the values are appearing correct. It is almost as if there is some sort of scaling issue</DIV>
<DIV dir=ltr>with values greater than 1. </DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>I have tried changing the pafScanline to a double and made the appropriate GDT_Float64 changes to GDALRasterIO and I get the same results.</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>Am I missing something fundamental here?</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>Thanks,</DIV>
<DIV dir=ltr>Bill<BR></DIV></NOSCRIPT>
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