WMS Server serving large raster

[Frank Warmerdam]

On 8/3/05, Dejan Gambin <dejan.gambin at pula.hr> wrote:
> Frank,
> 
> Back to old performance issues, I would like to know if making one big
> tiled output TIFF file with built overviews is better than having a set
> of tileindexed tiff files that each has built overviews (and even make
> each file tiled with -co TILED=YES)?
> 
> I am asking this because I have 18 80MB large tiff files (they don't
> form a square if merged). I have created overviews on each and used
> TILEINDEX. Now I am wondering if maybe is better to merge them using
> gdal_merge with -co TILED=YES and then build overviews on this one
> file??

Dejan, 

There is a certain amount of overhead to reading and parsing the
headers (and overview headers) of 18 files that I think might be 
noticable in a webmapping situation.  So views that show many of
the files (broad overview views) I think you would benefit from 
rebuilding everything as a single file with overviews. 

However, I have never done any real performance testing.  I do know
that the "header reading time" becomes significant when several dozens
of files need to be read for each render.  At 18 I am less sure that the
difference would be sigificant. 

Of course, the other issue is whether overview views are common.  If
most views are only one or two files then your current organization is
likely to be a bit better if only because the amount of "tile map" and
similar information needing to be loaded will be smaller than if one big
file was used.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent