[Gdal-dev] Re: urgent help needed

[Frank Warmerdam]

On 9/15/05, hina arif <hina192002 at yahoo.com> wrote:
>  
>  
> 
> hi i need help once again same is the way i am  working on .i mean the way i
> read the file is almost same but the problem is that when i read a file
> using GetRasterCount() it says that the file has only one band and then i
> read like that 
> 
> poBand->GetBlockSize(&nBlockXSize,&nBlockYSize);//resolution
> 
>  
> 
> pabyData = (GByte
> *)CPLMalloc(nBlockXSize*nBlockYSize*nBand*sizeof(GByte));//heap
> memory 
> 
> if(pabyData==NULL) error 
> 
>  
> 
> for(int i=0;i<poBand->GetBand();++i) 
> 
> e=poBand->ReadBlock(i,i,pabyData); 
> 


Hina,

You should not generally be using the ReadBlock() method. It
is mainly intended for low level applications.  

 > or i used  readIO like this 
> 
> e=poBand->RasterIO(GF_Read, 0,0,nBlockXSize,
> 0,pabyData,nBlockXSize,0,GDT_Byte,0,0); 
> 
> if i use value other than 0 an error comes and i think i am reading a band
> located at location 0,0 the first and only one 
> my file is of resolution 24810,784200 and its an black and white map image
> file 
> 
> sorry but i need ur assistance that what is an error in the code   

That is a large file!  Was there a particular reason you were trying
to read based on the block size?  The block size is basically the size
of a chunk in the file.  If you wanted to read just the first block you could
do that 

  poBand->RasterIO( GF_Read, 0, 0, nBlockXSize, nBlockYSize, 
                              pabyData, nBlockXSize, nBlockYSize,
GDT_Byte, 0, 0 );
 

I'm not sure which zero you were referring to changing .. there are several.

Best regards,
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