[Gdal-dev] [newbie] Reading of large TIF files

Tim Sutton tim at linfiniti.com
Thu Nov 10 04:32:24 EST 2005


Hi

Take a look at qgsrasterlayer.cpp in the QGIS (http://qgis.org)  
source code. We have already solved this problem.

Essentially, assign each of the three bands pixels to a different  
variable, then create a qcolor using each as the r,g,b values. Then  
simply paint your pixel using that qcolor.

OT I would be intersested to chat to you to see if a) the application  
you are working on is open source and b) you would be interested in  
combining efforts with QGIS.

Best Regards

Tim

On 10 Nov 2005, at 08:42, t.laue at web.de wrote:

> Dear all,
>
> I am currently developing a small application using Qt 4 and C++  
> for handling and
> evaluating large aerial images given in TIF / TIFF format. I am  
> using GDAL for image
> input. I am working with image overviews and image tiles for  
> providing a good zoom
> and pan performance.
>
> At the moment GDALRasterBand::RasterIO is being used for accessing  
> overview levels
> and reading small image patchs because I did not find a way how to  
> read from single
> overview levels using GDALDataset::RasterIO. Everything is working  
> fine as long as I
> am utilising gray value images with one raster band.
>
> In the case of RGB images I can employ a loop for retrieving the  
> data of all three raster
> bands from the same overview level resulting in three buffers which  
> contain the data. I
> would like to display the color image at the screen but I have no  
> idea how to combine
> them again.
>
> Is there a way to create a new dataset for adding the data read  
> from different bands? Is
> it possible to use GDALDataset to access single overview levels? Do  
> I have to use
> another method independent of GDAL to bring the three buffers  
> together in order to
> recreate a RGB image patch? Is anyone working with Qt 4 and GDAL?
>
> I am very thankful for every hint and idea.
>
> Best regards
>
> Thomas
>
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Tim Sutton (tim at linfiniti.com)

Visit http://qgis.org for a great open source GIS application
Skype : timlinux
Jabber : timlinux at jabber.org
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