The aggregate function
spoly( | edge); |
spoint edge;
can be used to create a polygon from a set of spherical points.
There are the same restrictions as for using the input function of
spherical polygon (see Section 3.8). The function
returns
NULL, if the polygon couldn't be created.
Example 4.7. Create a spherical polygon using a set of spherical points
Create a table and put in some spherical points with a unique ID. Then, create two polygons with different edge sequences.
sql> SELECT set_sphere_output('DEG');
set_sphere_output
-------------------
SET DEG
(1 row)
sql> CREATE TABLE points ( i int PRIMARY KEY, p spoint );
sql> INSERT INTO points VALUES (1, '( 0d, 0d)');
sql> INSERT INTO points VALUES (2, '(10d, 0d)');
sql> INSERT INTO points VALUES (3, '( 0d,10d)');
sql> SELECT spoly(data.p) FROM ( SELECT p FROM points ORDER BY i ASC ) AS data ;
spoly
-----------------------------------
{(0d , 0d),(10d , 0d),(0d , 10d)}
(1 row)
sql> SELECT spoly(data.p) FROM ( SELECT p FROM points ORDER BY i DESC ) AS data ;
spoly
-----------------------------------
{(0d , 10d),(10d , 0d),(0d , 0d)}
(1 row)