Basic GIS calculations that may be useful in Sahana eden:

• Centroid

  select name, asText(Centroid(the_geom)) from table where name='location';
  

• Bounding boxes

  select name, asText(Envelope(the_geom) from table where name='location';
  select name, extent(the_geom) from table where name = 'location' group by name;
  

• buffer calculations

• Distance - linear

  select distance(
  (transform(GeomFromText('Point(lon lat)'), 900913), 26915), 
  (transform(GeomFromText('Point(lon lat)'), 900913), 26915);
  

• Distance - Spherical

  select distance_sphere(
  (transform(GeomFromText('Point(lon lat)'), 900913), 
  (transform(GeomFromText('Point(lon lat)'), 900913);
  

• Distance - Spheroid

  select distance_spheroid(
  (GeomFromText('Point(lon lat)'), 900913), 
  (GeomFromText('Point(lon lat)'), 900913),
  'SPHEROID["GRS 1980", 6378137, 298.257222101]');
  

• intersections

  select name from location where
  GeomFromText('Point(lon lat)',900913)
  && the_geom AND
  within (GeomFromText('Point(lon lat)', 900913), the_geom);
  

• Point within polygon

  select name from location where
  GeomFromText('Point(lon lat)', 900913)
  && the_geom;