Raster tile indexing in PostGIS

[Frank Warmerdam]

Thy, Kristian wrote:
> From: percy [percyd at pdx.edu] 
>> My understanding is that shapefiles with a spatial index 
>> (qix, generated with the shptree utility in mapserver) are
>> actually faster than postgis access to the same data.
> 
> From: Fawcett, David [David.Fawcett at state.mn.us]
>> If you are looking for performance, I am guessing that you can
>> do better with spatially-indexed shapefiles.  Have you created
>> quadtree indexes for your tileindex shapefile?  Take a look at
>> shptree:
> http://mapserver.gis.umn.edu/docs/reference/utilityreference/shptree
> 
> Oh my.
> 
> Is this the general consensus? I.e. if I'm just using MapServer
> for displaying data and not using any of the spatial query
> stuff from PostGIS, I'm better off (performance-wise) with plain
> old shapefiles?

Kristian,

For simple cases the consensus is that shapefiles with a spatial
index are faster in mapserver than postgis is.  There are exceptions
of course, such as when you want to do attributes based queries which
cannot be indexed in shapefiles with mapserver.

> And if so, is the fact that ArcSDE is seemingly faster than
> plain old shapefiles just another ESRI license selling
> point to get people to shell out money for SDE? ;-)

It is hard to imagine that SDE is really faster for simple operations
than a shapefile unless they have made no effort to make shapefiles
fast.  I would presume the main selling points of SDE are about
shared access in a workgroup, "managability", and the ability to
do complicated RDBMS'ish things (like joins) efficiently.

> If yes, it's going to be hard to convince my bosses that we don't
> need the database, but I'll try :-)

You don't have to try too hard.  Postgres+postgis is still quite fast.
But if you are very performance sensitive and the other attributes aren't
important to you then shapefiles will generally be better for mapserver
feature data (and tileindexes).

Don't forget the spatial index though!

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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