WMS Server serving large raster

[Dejan Gambin]

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??

Of course, I can test it and see but...:-))

regards

dejan

-----Original Message-----
From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
Behalf Of Frank Warmerdam
Sent: Wednesday, August 03, 2005 3:06 PM
To: MAPSERVER-USERS at LISTS.UMN.EDU
Subject: Re: [UMN_MAPSERVER-USERS] WMS Server serving large raster


On 8/3/05, Milo van der Linden <mlinden at zeelandnet.nl> wrote:
> I indeed found the needed documentation on TILEINDEX and will try to 
> create it with gdaltindex. My raster images are however overlapping, 
> will this cause problems for the TILEINDEX since I think I remember 
> that ESRI shape files do not support overlapping objects (MapInfo 
> does)?

Milo, 

There is no problem having overlapping objects in a MapServer tileindex.
Shapefiles do allow overlapping polygons.  I think you are thinking of 
Arc/Info topological coverages which do not (normally). 

Note that overlapping files will be rendered in the order they are
processed which is normally the order in the shapefile though it will be
different if you build a spatial index for the tileindex file.  The last
file rendered "wins" being drawn over earlier data.  
   
> Will the requested 100x100 image be rebuild with every request sent 
> from a WMS client to the server? Because I tried it with a single 
> Raster Image in MapInfo via WMS Server and zooming in and out resulted

> in a loss of raster quality because the raster remained in the 
> resolution it had when it was first connected.

I don't know anything about MapInfo WMS client support, but it sounds as
if it requests the view once and then just keeps showing that same
raster.  As long as your "smart phone" re-requests new images from the
server they will be at the requested resolution. 

BTW, 1.5GB of raster imagery is quite modest and not demanding of
MapServer.  However some additional performance related steps may be
useful.  If you are going to be making some wide area requests to the
server (say for an overview of all holland) you will find it helpful to
pre-build overviews.  This can be accomplished on individual files using
the "gdaladdo" utility.  

But with such a modest amount of imagery, my suggestion would be to
build a merged mosaic file with all your imagery.  This might be
accomplished with the "gdal_merge.py" script.  Make sure you create a
tiled output TIFF file (-co TILED=YES) and then build overviews on it
with gdaladdo.  This will give you one file to list in your mapfile, and
maximize performance for overview views.  Other approachs (ie. tile
index with separate overviews layers in the mapfile) are also reasonable
but may be more work to setup.

Best regards,
-- 
---------------------------------------+--------------------------------
---------------------------------------+------
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