[Mapserver-users] Just call me a newbie . . . multiple Raster LAYERs question {Scanned} {Scanned}

[Ed McNierney]

Bob -

I'm surprised that you report bad experiences with TIFF imagery.  In
many respects, TIFF is the best uncompressed format to use for imagery.
I've got about 21 terabytes of it, all running under MapServer.

If you already have the data generated at multiple resolutions then I
don't think the GDAL approach will help much.  It really is simply a
different way of doing the same thing - prebuild the data at multiple
resolutions and preselect the most appropriate source.

GDAL has the benefit of storing the entire image pyramid in one TIFF
file, which makes file management and mapfile management easier, and it
also automatically chooses the best source resolution for each request,
so you don't need to calculate MINSCALE/MAXSCALE values.

The disadvantages are less flexibility in the resampling options (you
can choose from several GDAL algorithms, but you have to choose one of
them), inability to use externally-resampled images, files that are less
suitable for redistribution to others because they're larger (may or may
not be important), and less flexibility in adding/deleting resampled
levels.

But either way, TIFF images should be an excellent choice for storing
imagery.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com
(978) 251-4242 

-----Original Message-----
From: Bob Basques [mailto:bob.basques at ci.stpaul.mn.us] 
Sent: Thursday, March 18, 2004 11:01 AM
To: Mapserver List
Subject: Re: [Mapserver-users] Just call me a newbie . . . multiple
Raster LAYERs question {Scanned} {Scanned}

Ed McNierney wrote:

> Bob -
>  
> You can use GDAL to create TIFF overviews and produce the same effect 
> (multiple resolutions stored in one file) without the expense or 
> overhead of MrSID.  Your performance should be essentially identical 
> to using the multiple-LAYER approach.
>
I already have systems for generating the seperate tiles at each Level
of resolution.

The ranges are fairly extreme for the number of tiles per resolution
level.

9000+ tiles at 1/2 foot per pixel
down to
~16 tiles at 16 feet per pixel

I'm not sure how the performance can be increased at the server
(intranet installation, which typically means optimizing the server vs
the file transfers) using a combined lookup of some sort.

bobb

>  
>     - Ed
>
> Ed McNierney
> President and Chief Mapmaker
> TopoZone.com / Maps a la carte, Inc.
> 73 Princeton Street, Suite 305
> North Chelmsford, MA  01863
> ed at topozone.com
> (978) 251-4242
>
>
> ----------------------------------------------------------------------
> --
> *From:* blammo [mailto:bob.basques at ci.stpaul.mn.us]
> *Sent:* Thursday, March 18, 2004 9:06 AM
> *Cc:* Mapserver List
> *Subject:* Re: [Mapserver-users] Just call me a newbie . . . multiple 
> Raster LAYERs question {Scanned} {Scanned}
>
> Siki Zoltan wrote:
>
>>Hi,
>>
>>On Wed, 17 Mar 2004, Bob Basques wrote:
>>
>>  
>>
>>>All,
>>>
>>>Let's say I have Six different levels of resolution of Aerial Photo's

>>>all of them having the same coverage extents.
>>>
>>>
>>>    
>>>
>>
>>It won't work.
>>You should create six tile index and six layer and set MINSCALE and 
>>MAXSCALE for them to turn the best one for a scale. You can add them 
>>to the same group, so you can easily turn them on and off through the 
>>group name.
>>  
>>
> I got it to work as you (and others) described with seperate layers 
> and using the GROUP option.
>
>>An other solution may be the sid format (may be the ecw to).
>>As far as I know ecw is supported in the nightly built version.
>>As far as I know MrSid is not supported :( These format can contain 
>>multi resolution image sources, that case you can use the six 
>>different resolution tile as one image, that case no need for 
>>tileindex.
>>  
>>
> In my experience the MRSID option is too slow to render, I believe the

> performance is (much) better using the seperate resolutions as LAYERS.
>
> bobb
>

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