Definition
ST_IsRing takes an ST_LineString and returns 1 (Oracle and SQLite) or t (PostgreSQL) if it is a ring (for example, the ST_LineString is closed and simple); otherwise, it returns 0 (Oracle and SQLite) or f (PostgreSQL).
Syntax
Oracle and PostgreSQL
sde.st_isring (line1 sde.st_geometry)
SQLite
st_isring (line1 geometryblob)
Return type
Boolean
Example
The ring_linestring table is created with a single ST_LineString column, ln1.
The INSERT statements insert three linestrings into the ln1 column. The first row contains a linestring that's not closed and isn't a ring. The second row contains a closed and simple linestring that is a ring. The third row contains a linestring that is closed but not simple because it intersects its own interior. It is also not a ring.
The SELECT query returns the results of the ST_IsRing function. The first row returns 0 or f because the linestrings aren't rings, while the second and third rows return 1 or t because they are rings.
Oracle
CREATE TABLE ring_linestring (ln1 sde.st_geometry);
INSERT INTO RING_LINESTRING VALUES (
sde.st_linefromtext ('linestring (10.02 20.01, 10.32 23.98, 11.92 25.64)', 4326)
);
INSERT INTO RING_LINESTRING VALUES (
sde.st_linefromtext ('linestring (10.02 20.01, 11.92 35.64, 25.02 34.15, 19.15 33.94, 10.02 20.01)', 4326)
);
INSERT INTO ring_linestring (ln1) VALUES (
sde.st_linestring ('linestring (11 31, 11.25 31.12, 21.83 44.13, 16.45 44.24, 11 31)', 4326)
);
SELECT sde.st_isring (ln1) Is_it_a_ring
FROM RING_LINESTRING;
Is_it_a_ring
0
1
1
PostgreSQL
CREATE TABLE ring_linestring (ln1 sde.st_geometry);
INSERT INTO ring_linestring VALUES (
sde.st_linestring ('linestring (10.02 20.01, 10.32 23.98, 11.92 25.64)', 4326)
);
INSERT INTO ring_linestring VALUES (
sde.st_linestring ('linestring (10.02 20.01, 11.92 35.64, 25.02 34.15, 19.15 33.94, 10.02 20.01)', 4326)
);
INSERT INTO ring_linestring (ln1) VALUES (
sde.st_linestring ('linestring (11 31, 11.25 31.12, 21.83 44.13, 16.45 44.24, 11 31)', 4326)
);
SELECT sde.st_isring (ln1)
AS Is_it_a_ring
FROM ring_linestring;
Is_it_a_ring
f
t
t
SQLite
CREATE TABLE ring_linestring (id integer primary key autoincrement not null);
SELECT AddGeometryColumn (
NULL,
'ring_linestring',
'ln1',
4326,
'linestring',
'xy',
'null'
);
INSERT INTO ring_linestring (ln1) VALUES (
st_linestring ('linestring (10.02 20.01, 10.32 23.98, 11.92 25.64)', 4326)
);
INSERT INTO ring_linestring (ln1) VALUES (
st_linestring ('linestring (10.02 20.01, 11.92 35.64, 25.02 34.15, 19.15 33.94, 10.02 20.01)', 4326)
);
INSERT INTO ring_linestring (ln1) VALUES (
st_linestring ('linestring (11 31, 11.25 31.12, 21.83 44.13, 16.45 44.24, 11 31)', 4326)
);
SELECT st_isring (ln1)
AS "Is it a ring?"
FROM ring_linestring;
Is it a ring?
0
1
1