wiki:BluePrintGIStools

Version 3 (modified by Nico Presto, 11 years ago) ( diff )

expanded number of calcs with examples

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]');

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