[Gdal-dev] TIFF Driver & overviews

[Julien Demaria]

Hi,


I have some questions about the (Geo)TIFF GDAL driver :

- can we access to multi-directories TIFF ?
- can we access to sub-directories (using SubIFD tag) ?

- can I use existing overviews stored in a separate TIFF file or in the 
sub-directories ?
- In the code I see that the overviews are stored in directories after the 
first (the first is the full resolution image) ;
   can I store them in another place ? (example in another 
multi-directories TIFF file or inside the TIFF file but in the 
corresponding sub-directories of each directory) ?


General questions about overviews :

- do the drivers support not standard overviews ? (example full image 
100x200 and overview  43x17)

- I don't understand in the documentation if for an image 100x200 with 2 
overview 50x100 and 25x50 I can read directly a 30x60 buffer ?
   Is decimation read only allowed with the exact result size of an overview ?
   Can I read directly a 200x400 buffer in this image ?
   If yes can we control the pixels decimation/replication method ?

- for formats that don't support overviews does GDAL always store the 
overviews in another multi-directories TIFF file ?


sorry for the overflow of questions ;-)


Thanks in advance,

Julien