[Gdal-dev] Empty Tiles in GeoTIFFs

[Frank Warmerdam]

On 6/21/05, Tugrul Galatali <tugrul at galatali.com> wrote:
>         I've recently been working on a high resolution but sparse dataset that
> I've been storing in tiled GeoTIFFs. The bulk of the tiles are blank,
> and in my own software I just don't write these tiles to the file, and
> assume an error in reading one means it was blank to begin with. Which
> works great until I attempt to use a third party tool, including GDAL.
> 
>         Is what I'm doing a cheap hack I should never expect support for, and
> is there a raster format that does have explicit support for missing
> tiles?

Tugrul, 

Formats such as PCIDSK and Erdas Imagine do have explicit support
for missing tiles. 

It is also my intention that GDAL should treat a tile offset and tile size
of 0 as meaning a tile is NULL, though I haven't really made much use
of this concept.  

>         Also, after looking at a GeoTIFF generated by GDAL, and skimming the
> source and this list, it looks like TIFFTAG_GDAL_NODATA is a string of a
> single double, despite -src/dstnodata taking a value per band in
> gdalwarp. Is this the set definition for that tag, or is it bound to
> change in the future for multiple band support?

It may well change in the future.   

Best regards,
-- 
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