WMS Server serving large raster

[Gambin Dejan]

Thanks Frank very much,

I am aware of no significant difference in my case, I am asking this
just because of theoretical knowledge I would like to get. I only don't
understand completely the last issue you mentioned, about the 1-2 files
overviews and "tile map" information needing to be loaded. What does it
mean "if overview views are common" (maybe my "common" translation is
wrong)?

thanks and regards

dejan

-----Original Message-----
From: Frank Warmerdam [mailto:fwarmerdam at gmail.com] 
Sent: Thursday, August 04, 2005 4:36 AM
To: Gambin Dejan
Cc: MAPSERVER-USERS at lists.umn.edu
Subject: Re: [UMN_MAPSERVER-USERS] WMS Server serving large raster


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