[Gdal-dev] Can GDAL GDALDataset return compressed image data

[Lucena, Ivan]

I think that Frank gave you the all answers.

Frank Warmerdam wrote:
> Alison Luo wrote:
>> Hi Ivan,
>>
>> Thank you so much for your help. I have more questions
>> regarding the block of code you referred to in
>> nitifdataset.cpp. I also took a look of class
>> NITFSegmentInfo in nitflilb.h:
>>
>> NITFSegmentInfo has a member hAccess, which is the
>> NITF image stream.
> 
> Alison,
> 
> It is a pointer to the NITFImage structure for image segemnts.
> 
>  >  I suppose other pasSegmentInfo
>> member         GUInt32 nSegmentHeaderStart;
>>     GUInt32 nSegmentHeaderSize;
>>     GUInt32 nSegmentStart;
>>     GUInt32 nSegmentSize;
>> would somehow indicate how to get the encoded jpeg
>> stream from hAccess? Could you please explain how the
>> jpeg buffer is filled given this information?
> 
> They are information on where the image header, and image
> data chunks are in the file.  So compressed data stream
> would consist of nSegmentSize bytes started at byte nSegmentStart
> in the file.
> 
>> Why doesn't GDAL provide APIs to access encoded image
>> stream, but only provide API to get raw image stream?
> 
> GDAL does not provide direct access to compressed datastreams
> because the purpose of GDAL is to provide a "normalized" view to
> different datasets, not to provide low level access.
> 
> Best regards,