[xquery-talk] xquery and geospatial request

[Kev O'Neill]

You may also want to look at the functionality of pgSphere
(http://gborg.postgresql.org/project/pgsphere/projdisplay.php), another
Postgres extension specifically to cover spherical co-ordinates.

This is one of a small number of packages that can cope with things like
polygons covering at least one pole and/or the date line, things that cause
PostGIS and OracleGIS to display 'idiosyncracies' ;-)

Also, the work by OGC/ISO TC211 is worth looking at.

Cheers,
   Kev
-----Original Message-----
From: talk-bounces at x-query.com [mailto:talk-bounces at x-query.com] On Behalf
Of Jeff Dexter
Sent: 01 June 2007 20:28
To: 'Ken North'; talk at x-query.com
Subject: RE: [xquery-talk] xquery and geospatial request


Our approach in the TigerLogic XDMBS was to integrate in R-Tree indexes and
then essentially treat any GML fragment within documents as "special", and
capable of being registered into the index. This means the GML can be
embedded and queried anywhere in the document, mixed with any other type of
XML, images, etc. We then present spatial comparisons as XQuery functions
(similar to how the spatial operators are defined in spatial-enabled SQL
engines) so they can be mixed with standard XQuery, full-text, etc.

GML works nicely with XQuery and the indexing since it allows the engine to
determine what to index, and it can be nested anywhere in an XML document.
Furthermore, XQuery, with some additional functions to convert from the
Well-Known Text/Binary formats used in other engines, is quite useful for
building new GML on the fly, and parsing/validating existing GML.

Jeff. 

-----Original Message-----
From: talk-bounces at x-query.com [mailto:talk-bounces at x-query.com] On Behalf
Of Ken North
Sent: Friday, June 01, 2007 12:08 PM
To: talk at x-query.com
Subject: Re: [xquery-talk] xquery and geospatial request

> I need to store GML feature in  a database and to be able to make
> geospatial request on them.
>
> Do we have a language (extension to xquery) to make such request on a
> XML native database ?

For an engine to store and retrieve geospatial data, it needs to operate
with metadata for geospatial information and use something like R-tree
indexing to provide query performance. Then there might be a requirement to
do content-based image retrieval and support OpenGIS data types.

Support for geospatial processing has matured in platforms such as Informix
Spatial DataBlade, Oracle Spatial, DB2 Spatial and ESRI SDE. It would be
bleeding edge for a native XML database with limited indexing capability.
(B-tree indexing is adequate for alphanumeric types but not for geospatial
data.)

Oak Ridge National Labs has done some interesting work on indexing
geospatial data. It uses a markup agent to create an XML file with
properties and metadata for each satellite image. Another agent uses those
XML files when analyzing the images to create feature vectors for segment
clustering and index creation.

You might want to look at something like the PostGIS extension for
PostgreSQL. It's used for GeoServer, available with a GPL license, and
supports R-tree indexing. There's also an open source product for using
spatial types with Microsoft SQL Server. A client seems happy with the Java
Topology Suite and GeoTools, which includes a GML parser.

PostGIS
http://postgres.refractions.net

JTS, GeoTools http://docs.codehaus.org/display/GEOS/SpatialDBBox
http://geotools.codehaus.org/Extending+The+XML+Parser

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