[gdal-dev] python-gdal ComputStatistics return just two values

[Even Rouault]

Le Friday 27 March 2009 20:05:11 Lucena, Ivan, vous avez écrit :
> Even,
>
> I see. You are right. With the absence of ComputeRasterStatistics() I got
> confused and I made the wrong
>
> assumption. BTW, why there is no wrapper for ComputeRasterStatistics()? That 
would work then:
> >>> bd1.SetStatistics(bd2.ComputeRasterStatistics())

Because you don't use the latest and greatest GDAL ;-)

Extract from swig/include/Band.i from SVN head:

  /* Interface method added for GDAL 1.7.0 */
%apply (double *OUTPUT){double *min, double *max, double *mean, double 
*stddev};
%apply (IF_ERROR_RETURN_NONE) { (CPLErr) }; 
  CPLErr ComputeStatistics( bool approx_ok, double *min = NULL, double *max = 
NULL, double *mean = NULL, double *stddev = NULL,                          
GDALProgressFunc callback = NULL, void* callback_data=NULL){
    return GDALComputeRasterStatistics( self, approx_ok, min, max, mean, 
stddev, callback, callback_data );
  }
%clear (CPLErr);


>
> Not a big deal. The work around is easy.
>
> Thank you very much,
>
> Ivan
>
> >  -------Original Message-------
> >  From: Even Rouault <even.rouault at mines-paris.org>
> >  Subject: Re: [gdal-dev] python-gdal ComputStatistics return just two
> > values Sent: Mar 27 '09 18:45
> >
> >  Hi Ivan,
> >
> >  I don't think there's a bug.
> >
> >  The C API for ComputeBandStats is :
> >
> >  CPLErr CPL_DLL CPL_STDCALL
> >  GDALComputeBandStats( GDALRasterBandH hBand, int nSampleStep,
> >                               double *pdfMean, double *pdfStdDev,
> >                               GDALProgressFunc pfnProgress,
> >                               void *pProgressData );
> >
> >  So, the python API is consistant with it.
> >
> >  So it is expected that "bd1.SetStatistics(bd2.ComputeBandStats())" will
> > fail as it is provided with 2 values instead of the expected 4.
> >
> >  Best regards,
> >  Even
> >
> >  Le Friday 27 March 2009 19:02:14 Lucena, Ivan, vous avez écrit :
> >  > Hi there,
> >  >
> >  > I believe that ComputeBandStats() should return 4 values min, max,
> >  > mean and stddev) [1] but the Python API is returning just mean and
> >  > stddev.
> >  >
> >  > python:
> >  > >>> bd.ComputeBandStats()
> >  >
> >  > (9.0071713001936118, 11.350094331448236)
> >  >
> >  > >>> bd.ComputeRasterMinMax()
> >  >
> >  > (-1.7899999618530273, 31.149999618530273)
> >  >
> >  > gdalinfo:
> >  >
> >  > Band 1 Block=360x1 Type=Float32, ColorInterp=Gray
> >  >   Min=-1.790 Max=31.150
> >  >   Minimum=-1.790, Maximum=31.150, Mean=9.007, StdDev=11.350
> >  >   Unit Type: unspecified
> >  >   Metadata:
> >  >     STATISTICS_MINIMUM=-1.789999961853
> >  >     STATISTICS_MAXIMUM=31.14999961853
> >  >     STATISTICS_MEAN=9.0071713001936
> >  >     STATISTICS_STDDEV=11.350094331448
> >  >
> >  > Is that a bug?
> >  >
> >  > See what happens in that case:
> >  > >>> bd1.SetStatistics(bd2.ComputeBandStats())
> >  >
> >  > Traceback (most recent call last):
> >  >   File "<interactive input>", line 1, in <module>
> >  >   File "E:\Python25\Lib\site-packages\osgeo\gdal.py", line 729, in
> >  > SetStatistics return _gdal.Band_SetStatistics(*args)
> >  > TypeError: Band_SetStatistics() takes exactly 5 arguments (2 given)
> >  >
> >  > My best regards,
> >  >
> >  > Ivan
> >  >
> >  > [1] http://www.gdal.org/gdal_8h.html#a93b6b6ea6e71017ce25524e1a9ef1e3
> >  >
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