[OSGeo-Discuss] Re: Raster data on RDBMS

[Sylvan Ascent Inc.]

Well, now we get to the crux of the matter, what are the benefits? Let's analyze this a bit more to see if anything seems important. You mention:
 
1) Spatial Extension - not sure what this is, but maybe you can build image operations into the database.
2) Schemas - Schemas can be queried, put into views, massaged
3) Metadata - well that's always handy, and likely much easier to maintain and query in a database.
4) Georeferences definition - Right, like simple features georeferencing, built into the schema
5) Spatial Indexation - Could make tiles faster to retrieve, coupled with pyramiding, should be decent performance
 
I'll add this:
6) As newer data comes in you can more easily upgrade a raster coverage, as the metadata (like the date) can be queried for the latest and greatest, while retaining the older stuff. This might be trickier in a file based system.
 
and how about the usual rdbms stuff like
7) Replication - might be useful once in a while, esp in big systems
8) Scalability (not sure exactly if this is the word, but db vendors/OS projects have put a lot of effort into scaling over lots of users)
9) Backup
 
10) Transactions, possibly, if you are bringing raster data in from a satellite and something goes wrong? Unlikely to be to much of a benefit though.
11) Potentially more robust than using a file system
 
More anyone? How about disadvantages, like
 
1) You have to import the raster data into the database.
2) Have to decide what format/projection/datum to use to store the data.
3) Possibly more storage is used, but these days who cares?
4) Tile edge effects (with most compression schemes, there is often a noticeable "joint" when joining two tiles)
5) Partial tiles - when you split up an image, it rarely fits perfectly into your chosen tile size. What do you do with the leftovers?
 
More?
 
Another 2 cents,
 
Roger 

________________________________

From: discuss-bounces at lists.osgeo.org on behalf of Lucena, Ivan
Sent: Fri 10/31/2008 1:20 AM
To: OSGeo Discussions
Subject: Re: [OSGeo-Discuss] Re: Raster data on RDBMS



Paul,

That is not the answer your are waiting for but...

IMHO, once you overcome the mythical concept that a database server will always perform slower than a direct file access then "Spatial is not special anymore!" [who said that?] and you can think on the benefits just like a banker or an accounting bureau. Database servers in general are capable of making a good use of the available resources. For raster what is needed is a good BLOB support with cursor preferably. Spatial extension and schemas are indispensable accessories, they should provide metadata, georeferences definition, spatial indexation, etc. but they should not drag down the performance.

Just my two cents.

Ivan

>  -------Original Message-------
>  From: Paul Ramsey <pramsey at cleverelephant.ca>
>  Subject: Re: [OSGeo-Discuss] Re: Raster data on RDBMS
>  Sent: Oct 31 '08 02:11
>  
>  On Thu, Oct 30, 2008 at 5:25 PM, Gilberto Camara
>  <gilberto.camara at inpe.br> wrote:
>  > but the benefits of having
>  > raster data on a DBMS are much more important.
>  
>  And those benefits are....?
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>  Discuss mailing list
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