[Gdal-dev] using gdaladdo with tiled tifs

[Frank Warmerdam]

Jeff Hoffmann wrote:
> I have a question about the best way to create overviews in tiled tifs. 
>    I've created my tifs with a block size of 512x512 with the 
> understanding that this should help with performance if I'm pulling 
> small blocks (say 500 x 500 pixels) from much larger images (say 20k x 
> 20k pixels).  So when I created that tif, I passed a bunch of command 
> line configuration options to gdal_translate to get the tiling I 
> selected, but when I did overviews, I just did a plain "gdaladdo my.tif 
> 2 4 8 16 32" without any options.  Should I be telling gdaladdo all of 
> the same tiling options as when I created the tif?  

Jeff,

I don't think you have much control over options used to create the
overviews.  I believe GDAL by default uses a 256x256 tile size for
overviews which should be ok in your situation.

 > Or does it just know
> to use the same configuration as when it was created?  Or doesn't it 
> matter?  Also, I've chosen to compress the original tif because most of 
> the usage will come from the overviews.  Do I need to tell it not to 
> compress the overviews or is that the default and I actually have to 
> tell it to compress the overviews?

I *think* GDAL uses the same compression type for overviews as for the
main image which should be OK, though if you prefer not to have the overviews
compressed, I'm not sure that provides a way of controlling it.

Best regards,
-- 
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