PostGIS Cookbook - Second Edition

Getting ready

We will start by creating another table of random points with x, y, and z values, as shown in the following query:

DROP TABLE IF EXISTS chp02.xwhyzed1 CASCADE; 
CREATE TABLE chp02.xwhyzed1 
( 
  x numeric, 
  y numeric, 
  z numeric 
) 
WITH (OIDS=FALSE); 
ALTER TABLE chp02.xwhyzed1 OWNER TO me; 
ALTER TABLE chp02.xwhyzed1 ADD COLUMN gid serial; 
ALTER TABLE chp02.xwhyzed1 ADD PRIMARY KEY (gid); 
 
INSERT INTO chp02.xwhyzed1 (x, y, z) 
  VALUES (random()*5, random()*7, random()*106); 
INSERT INTO chp02.xwhyzed1 (x, y, z) 
  VALUES (random()*5, random()*7, random()*106); 
INSERT INTO chp02.xwhyzed1 (x, y, z) 
  VALUES (random()*5, random()*7, random()*106); 
INSERT INTO chp02.xwhyzed1 (x, y, z) 
  VALUES (random()*5, random()*7, random()*106);