tryagaaa (1) [Avatar] Offline
#1
I am reading the book "PostGIS In Action"

and now I follow the listing 2.4 here

SELECT AddGeometryColumn ('public','my_geometries',
'my_circular_strings',-1,'CIRCULARSTRING',2);
INSERT INTO my_geometries(name,my_circular_strings)
VALUES ('Circle',
ST_GeomFromText('CIRCULARSTRING(0 0,2 0, 2 2, 0 2, 0 0)')),
('Half Circle',
ST_GeomFromText('CIRCULARSTRING(2.5 2.5,4.5 2.5, 4.5 4.5)')),
('Several Arcs',
ST_GeomFromText('CIRCULARSTRING(5 5,6 6,4 8, 7 9, 9.5 9.5,
11 12, 12 12)'));
And out put as

SELECT name,ST_NPoints(my_circular_strings) As cnpoints,
ST_NPoints(ST_CurveToLine(my_circular_strings)) As lnpoints
FROM my_geometries
WHERE my_circular_strings IS NOT NULL;
and postgresql give me a table

name | cnpoints | lnpoints
----------------------------------------------------+----------+----------
Circle | 5 | 129
Half_Circle | 3 | 65
Several Arcs | 7 | 113
(3 rows)
My question is the book also give me a figure as result


I want to make a picture like that ,how to do it??