[Gdal-dev] using gdaladdo with tiled tifs

[Jeff Hoffmann]

Frank Warmerdam wrote:
> 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.

Thanks for the quick reply, Frank.  I've made up a few files like I said 
& the performance seems fine that way, I was just wondering if I should 
be doing anything else before going off and processing several hundred 
GBs of tifs.

>  > 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.

Actually, I guess with fairly small tiles compressed overviews may not 
be such a bad thing since I won't be particularly CPU-constrained and 
they should decompress pretty quickly.  Maybe some benchmarking might be 
in order.  I think the thing that got me wondering this is that you 
don't really see much information about the overviews other than their 
size so I guess I just always assumed they replicated the settings of 
the original image.

-- 
Jeff Hoffmann
Head Plate Spinner
PropertyKey.com