Changes between Version 12 and Version 13 of BluePrintGISStorage

Timestamp:

06/20/11 18:39:18 (14 years ago)

Author:

Fran Boon

Comment:

--

BluePrintGISStorage

@@ -39 +39 @@
 
 Q: copy [http://docs.djangoproject.com/en/dev/ref/contrib/gis/db-api/ GeoDjango]?
+
+== Extend DAL to support Spatial Queries ==
+We need to support some extra SQL queries in DAL.
+
+I guess we have a PostGIS Adapter which inherits from the PostgreSQL one & a Spatialite adapter which inherits from the Sqlite one.
+
+Both should inherit the OpenGIS set of SQL syntax
+
+
+We need to be able to do spatial queries like this:
+* http://postgis.refractions.net/docs/ST_Overlaps.html
+This one is our key performance bottleneck currently as we do BBOX filters on GeoJSON feature layers like this:
+* http://bazaar.launchpad.net/~flavour/sahana-eden/trunk/view/head:/modules/s3/s3rest.py#L1773
+Instead of this query:
+{{{
+bbox_filter = ((db.location.lon > minLon) & (db.location.lon < maxLon) & (db.location.lat > minLat) & (db.location.lat < maxLat))
+}}}
+We want to:
+{{{
+bbox_filter = (db.location.ST_Overlaps([minLon, minLat, maxLon, maxLat]))
+}}}
+
+Full list of possible commands are here, but I don't expect all these to be implemented immediately (we can add additional ones as/when we need them if the hooks are right):
+* http://postgis.refractions.net/documentation/manual-1.3/ch06.html#id2574404
+
+
+We could also want to be able to specify that a table is spatialised, so an option to db.define_table(spatial=True).
+If this is on then we should send AddGeometryColumn() to the SQL Adapter
+
+NB A normal system would commonly only have a single spatial table, so this could be easily done out of band using a script, as I do now:
+* wiki:InstallationGuidelinesPostgreSQL#AddGeometrycolumntogis_location
+
+
+There are also some new field types, but I don't think we need to worry about those right now.
+
+Full specs are here:
+* http://www.opengeospatial.org/standards/sfs
+
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 [wiki:BluePrintGeographicInformationSystems GIS BluePrints]