Re: [gdal-dev] [GDAL dev][GDALRasterBand::IReadBlock] About how to read all the raster bands.

[Lucena, Ivan]

Hi There,

I am not quite sure that I understood your problem, but I am pretty sure that you can write whatever bock size you 
want. On the "GDAL implementation tutorial" [1] you should that especial attention to fill up those attributes:

GDALDataset::nRasterXSize
GDALDataset::nRasterYSize
GDALRasterBand::nBlockYSize
GDALRasterBand::nBlockXSize
GDALRasterBand::eDataType

That will tell how GDAL will handle its internal block buffers.

You can take a look at one of the drivers that I wrote as example:

http://trac.osgeo.org/gdal/browser/trunk/gdal/frmts/idrisi/IdrisiDataset.cpp#L500
http://trac.osgeo.org/gdal/browser/trunk/gdal/frmts/idrisi/IdrisiDataset.cpp#L1261

Regards,

Ivan



>  -------Original Message-------
>  From: Cherif Oueslati <oueslati.cherif at gmail.com>
>  Subject: [gdal-dev] [GDAL dev][GDALRasterBand::IReadBlock] About how to read	all the raster bands.
>  Sent: Oct 10 '08 07:22
>  
>  Hello,
>  
>  
>  I am implementing a format specific driver to add new format. So i have to
>  read raster bands from a file in addition of the metadata given in the
>  header.
>  
>  The gdalinfo.exe is working effeciently, by using an OGRSpatialReference
>  object. However i found a problem with the gdal_translate.exe application.
>  
>  
>  In fact, and when debugging, an error appears indicating that it's
>  impossible to write in certain memory address, knowing that the input file
>  to read contain 501 pixels (corresponding to nBlockXSize) and 501 lines
>  (corresponding to nBlockYSize).
>  
>  To avoid this problem, i changed the number of iterations in the for loop,
>  which is allowing reading all the raster bands and filling into the pImage,
>  from (nBlockXSize*nBlockYSize) to (nBlockXSize*125).
>  
>  As a consequence i obtain an image that is a part of the whole image to
>  read which is logic, since i'm not putting all the raster bands.
>  
>  
>  So to summarise the problem: (nBlockXSize*125) is the maximum rows that i
>  can put into the destination file image or i have to use all the
>  (nBlockXSize*nBlockYSize) raster bands.
>  
>  I think that it's related to the default size of the destination file
>  image.
>  
>  I used CPLMalloc, CPLRealloc, memset and memcpy functions but it was
>  fruitless. Could you tell me how to modify this default size?
>  
>  Otherwise have you any other suggestions.
>  
>  
>  With all my regards.
>  
>  Cherif OUESLATI
>  --------------------
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