Re: [gdal-dev] Writing pixel values

[Ivan Lucena]

Akhil,

If you loo at that section of the API Tutorial:

"Using CreateCopy()

The GDALDriver::CreateCopy() method can be used fairly simply..."

You will see that what you need to do is to call GDALOpen() with GA_ReadOnly passing the input file; then you would need to get a driver, with GDALGetDriverByName(); then call GDALCreateCopy() passing the driver and the output file name.

That returns the output dataset pointer read for writing. You don't need to call GDALOpen with GA_Update in that case.

You should call GDALGetRasterBand() from the input dataset and from the output dataset.

You can find example of that on the last "In C: " source code box on the GDAL API tutorial.

Please pay attention to what Frank said about the number of pixels that you are trying to write. He is the boss. :)

By the way, I am planning to visit RIT this fall with my son. What Al Pacino and Graig Ferguson are going to be doing together over there? :) (rit.edu).

Regards,

Ivan

>  -------Original Message-------
>  From: Akhil Jaggarwal <axj4159 at cs.rit.edu>
>  To: gdal-dev at lists.osgeo.org
>  Subject: Re: [gdal-dev] Writing pixel values
>  Sent: Sep 15 '10 14:14
>  
>  Thanks, I understand what I was doing wrong and have appropriately
>  made some changes.
>  
>  I created a new band to write using:
>  
>  GDALRasterBandH hDestBand;
>  
>  and open the dataset for writing:
>  
>  hDestDS = GDALOpen( pszDestFileName, GA_Update );
>  
>  
>  Then I pass metadata:
>  hDestDS = GDALCreateCopy( hDriver, pszDestFileName, hDataset, FALSE,
>                                        NULL, NULL, NULL );
>  
>  And read all the dataset into pafscanfile buffer: (before starting the for loop)
>  GDALRasterIO(hBand, GF_Read, 0, 0, nxSize, nySize,
>                          pafScanline,
>                          nxSize,nySize,
>                          GDT_Int16,
>                          0, 0);
>  
>  However, when it comes to the part of writing the dataset, using:
>    for(i = 0; i < nySize; i++) {
>                  for(j = 0; j < nxSize; j++) {
>                           if( CE_Failure == GDALRasterIO( hDestBand,
>  GF_Write, j, i, 1, 1,
>                            change1, 1, 1 , GDT_Int16, 0,0) ) {
>                                    printf("Write Error!");
>                                    return 1;
>                            }
>  
>  I get the error:
>  
>  ERROR 5: Access window out of range in RasterIO().  Requested
>  (1,1) of size 1x1 on raster of 0x0.
>  Write Error
>  
>  What am I missing here? It seems I 've to specify the the raster band
>  size of the ouput band. How can I do that?
>  
>  Thanks once again.
>  
>  On Wed, Sep 15, 2010 at 11:58 AM, Ivan Lucena <ivan.lucena at pmldnet.com> wrote:
>  > Akhil,
>  >
>  > How did you create or opened the output? Did you also create the bands before calling GDALRasterIO?
>  >
>  > See examples on: http://gdal.org/gdal_tutorial.html
>  >
>  > Regards,
>  >
>  > Ivan
>  >
>  >
>  >>  -------Original Message-------
>  >>  From: Akhil Jaggarwal <axj4159 at cs.rit.edu>
>  >>  To: gdal-dev at lists.osgeo.org
>  >>  Subject: [gdal-dev] Writing pixel values
>  >>  Sent: Sep 15 '10 10:52
>  >>
>  >>  Hi,
>  >>
>  >>  Any comments/suggestions on this issue would be immensely helpful!
>  >>
>  >>  I'm storing the pixel values in a buffer like this:
>  >>
>  >>  pafScanline = (short int*)CPLMalloc(sizeof(short int)*nxSize*nySize);
>  >>
>  >>  I can read the data alright. The call to GDALRasterIO is being made
>  >>  correctly, which I do with:
>  >>
>  >>  GDALRasterIO(hBand, GF_Read, 0, 0, nxSize, nySize,
>  >>                         pafScanline,
>  >>                         nxSize,nySize,
>  >>                         GDT_Int16,
>  >>                         0, 0);
>  >>  However, when it comes to the part of writing a pixel data to an
>  >>  output file, the call to GDALRasterIO fails:
>  >>
>  >>  for(i = 0; i < nySize; i++) {
>  >>                 for(j = 0; j < nxSize; j++) {
>  >>
>  >>                         if( CE_Failure == GDALRasterIO( hDestDS,
>  >>  GF_Write, 0, 0, j, i,
>  >>                           change1, j, i , GDT_Int16, 0,0) ) {
>  >>                                   printf("Write Error!");
>  >>                                   return 1;
>  >>                           }
>  >>               }
>  >>    }
>  >>
>  >>  Where change1 is a variable to hold pixel data that I want to change.
>  >>  It's declared in the following manner:
>  >>
>  >>  short int*change1;
>  >>  change1 = malloc(sizeof(short int));
>  >>  *change1 = 1;
>  >>
>  >>  I can't get what exactly am I missing. The file i'm using is a tiled,
>  >>  16 bit signed TIFF.
>  >>
>  >>  How do I change the value at a pixel location?
>  >>
>  >>  Thanks!
>  >>  _______________________________________________
>  >>  gdal-dev mailing list
>  >>  gdal-dev at lists.osgeo.org
>  >>  http://lists.osgeo.org/mailman/listinfo/gdal-dev
>  >>
>  >
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