How can I display with OpenLayers the geometry returned from a ST_Buffer in POSTGIS?

Question

Im using PostGIS, GeoServer and OpenLayers, and the thing is that i want to display the geometry result from a query like this:

SELECT ST_Buffer(ST_GeomFromText('POINT(100 100)'), 500);

To perform queries I'm using Java, the line I use to perform a query is the following:

resulset = statement.executeQuery(query);

where resulset is a ResulSet type object, when I convert it to String I get the following:

org.postgresql.jdbc4.Jdbc4ResultSet@163b102

My question is how do I interpret that to display the POLYGON I suppose is in there in a layer? or am I doing something wrong? Hope someone can help me with this question, thanks.

Answer 1

You can perform operations with WKT you return from consultations in postgis

SELECT ST_ASTEXT(ST_Buffer(ST_GeomFromText('POINT(100 100)'), 500));

you recieve WKT and use Openlayer to convert the wkt to geometry and feature. for example : var elemento = New OpenLayers.Format.WKT().read('textWktFromRecordColumn');

I hope it helps. greetings

Answer 2

Have a look at the WPS addon for GeoServer - http://docs.geoserver.org/stable/en/user/extensions/wps/processes.html which provides a clean interface for this sort of query.

Answer 3

if you use geodjango from server side, you can achieve this with performing raw SQL queries...

for example :

with models in model.py

Person.objects.raw('''SELECT ST_Buffer(ST_GeomFromText('POINT(100 100)'), 500);''');

or importing some module for connection and directly querying:

from django.db import connection, transaction
cursor = connection.cursor()

cursor.execute(SELECT ST_Buffer(ST_GeomFromText('POINT(100 100)'), 500))
row = cursor.fetchone() # .fetcall()

this is data retrievalling work for executing raw sql...

and last word about this geoquery