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 measurements

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

• 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;

• Spherical distance

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

• Spheroid distance

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