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| Subject: | RE: GISList: Working with large rasters ~100Gb and GIS |
| Date: |
03/17/2003 10:17:19 AM |
| From: |
Voets, D. |
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Dear Uffe and others,
It greatly depends on the type of data you are loading. ArcSDE supports a
number of compression techniques, and these compression techniques may
greatly reduce the amount of data stored. However, the compression
techniques can be relatively to very ineffective compared to uncompressed
data, depending on the type of data. Scanned maps and vector data generated
images can greatly benefit from a compression type like LZ77. Areal
photographs etc very often increase in size using LZ77, compared to
uncompressed. ArcSDE also supports a JPEG lossy compression scheme, and that
will compress areal photographs quite well. The drwback of that approach is
that JPEG is lossy, and it is much more lossy than MrSID and ECW are.
So, there are a number of factors that greatly influence the resulting size
in the database. these factors are:
- the compression in the original file. TIFF input files can be
uncompressed, but they can also be stored as Packbits compressed, LZW
compressed, Fax Group 3 and 4 compressed, even JPEG compression can be used
within a TIFF file.
- The type of data in the original files. vector generated images and
scanned maps are always easier to compress than areal photographs are, if
you want to keep the quality comparable to the original data.
- the compression scheme you choose in the database.
- the type of database. Though I'm not sure about this, I get the impression
that Oracle tends to be a bit more compact than for instance SQLserver.
However, I may be mistaken there.
The discussion is indeed very interesting. Storing and providing to an
organization 100GB of areal photographs is quite uncommon (yet), there is no
silver bullet that will do the overall trick. I am curious to know the
outcome.
All the best,
Dirk Voets
Support Engineer
ESRI Nederland B.V.
Tel : 010 - 217 07 50
Email : GISsupport@esrinl.com
Internet : http://www.esrinl.com
Call aanmelden via Internet: http://www.esrinl.com/ondersteuning/callNL.asp,
FAQ's op: http://www.esrinl.com/ondersteuning/vragen.asp
-----Original Message-----
From: Uffe Kousgaard [mailto:uffe@routeware.dk]
Sent: Friday, March 07, 2003 3:50 PM
To: GIS Community
Subject: Re: GISList: Working with large rasters ~100Gb and GIS
From: "Voets, D." <D.Voets@esrinl.com>
> ArcSDE will basically be able to load all that data, but it will put
> tremendous constraints on the database you use. This may not be the
easiest
> way to handle your data. There aren't too many databases and servers
that
> can handle this. Your data would probably double or triple, because of
> indexes and storage procedures in the database.
I have loaded 550 Mb of GeoTIFF files (PackBits compressed) into ArcSDE
8.2 on Oracle 8.1.7. That resulted in a 110 Mb increase in used space on
the server, so I can't really recognize your double/triple? This was
including pyramids and using LZ77 compression (loss-less).
Since I'm about to load a total of 30 Gb of TIFF files, I find this
discussion very interesting.
Regards
Uffe Kousgaard
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