Hello,
With PostgreSQL 10.11, I was trying to compare a circle made with the function
circle() to the « same » or similar one made thanks to the function
ST_Buffer().
-> The circle of type circle : circle('POINT(1 2)'::geometry::point,
0.5::double precision) :
SELECT ST_AsText(polygon(32, circle('POINT(1 2)'::geometry::point, 0.5::double
precision))::geometry) AS circle_cast_as_polygon ;
circle_cast_as_polygon
-------------------------------------------------------------------------------------------
POLYGON((0.5 2,0.509607359798385 2.09754516100806,0.538060233744357
2.19134171618254,0.584265193848727 2.2777851165098,0.646446609406726
2.35355339059327,0.722214883490199 2.41573480615127,0.808658283817455
2.46193976625564,0.902454838991936 2.49039264020162,1 2.5,1.09754516100806
2.49039264020162,1.19134171618254
2.46193976625564,1.27778511650982.41573480615127,1.35355339059327
2.35355339059327,1.41573480615127 2.2777851165098,1.46193976625564
2.19134171618254,1.49039264020162 2.09754516100806,1.5
2,1.490392640201621.90245483899194,1.46193976625564
1.80865828381746,1.41573480615127 1.7222148834902,1.35355339059327
1.64644660940673,1.2777851165098 1.58426519384873,1.19134171618255
1.53806023374436,1.09754516100806 1.50960735979838,1 1.5,0.902454838991936
1.50960735979838,0.808658283817455 1.53806023374436,0.722214883490199
1.58426519384873,0.646446609406726 1.64644660940673,0.584265193848727
1.7222148834902,0.538060233744357 1.80865828381745,0.509607359798385
1.90245483899194,0.5 2))
-> The circle of polygon sub-type : ST_Buffer('POINT(1 2)'::geometry,
0.5::double precision) :
SELECT ST_AsText(ST_Buffer('POINT(1 2)'::geometry, 0.5::double precision)) AS
circle_as_polygon_via_ST_Buffer ;
circle_as_polygon_via_st_buffer
-------------------------------------------------------------------------------------------
POLYGON((1.5 2,1.49039264020162 1.90245483899194,1.46193976625564
1.80865828381746,1.41573480615127 1.7222148834902,1.35355339059327
1.64644660940673,1.2777851165098 1.58426519384873,1.19134171618255
1.53806023374436,1.09754516100806 1.50960735979838,1 1.5,0.902454838991937
1.50960735979838,0.808658283817456 1.53806023374436,0.7222148834902
1.58426519384873,0.646446609406727 1.64644660940673,0.584265193848728
1.7222148834902,0.538060233744357 1.80865828381745,0.509607359798385
1.90245483899193,0.5 2,0.509607359798384 2.09754516100806,0.538060233744356
2.19134171618254,0.584265193848726 2.2777851165098,0.646446609406725
2.35355339059327,0.722214883490197 2.41573480615127,0.808658283817453
2.46193976625564,0.902454838991934 2.49039264020161,0.999999999999998
2.5,1.09754516100806 2.49039264020162,1.19134171618254
2.46193976625564,1.2777851165098 2.41573480615127,1.35355339059327
2.35355339059327,1.41573480615127 2.2777851165098,1.46193976625564
2.19134171618255,1.49039264020161 2.09754516100807,1.5 2))
Comparison :
SELECT ST_OrderingEquals(ST_Buffer('POINT(1 2)'::geometry, 0.5::double
precision) , polygon(32, circle('POINT(1 2)'::geometry::point, 0.5::double
precision))::geometry) ;
st_orderingequals
-------------------
f
-> OK, with an ordering polygon equality
=> But, I was surprised by the result of the following 2 SQL queries, in
particular by the second one :
SELECT ST_Equals(ST_Buffer('POINT(1 2)'::geometry, 0.5::double precision) ,
polygon(32, circle('POINT(1 2)'::geometry::point, 0.5::double
precision))::geometry) ;
st_equals
-----------
f <= weird for me !
SELECT ST_Buffer('POINT(1 2)'::geometry, 0.5::double precision) = polygon(32,
circle('POINT(1 2)'::geometry::point, 0.5::double precision))::geometry AS
BounderingEquals ;
bounderingequals
------------------
f <= weird for me !
Details (OK) :
SELECT box(polygon(32, circle('POINT(1 2)'::geometry::point, 0.5::double
precision))::geometry) AS box_from_circle_through_polygon ;
box_from_circle_through_polygon
---------------------------------
(1.5,2.5),(0.5,1.5)
SELECT box( ST_Buffer('POINT(1 2)'::geometry, 0.5::double precision)) AS
box_from_ST_Buffer_polygon ;
box_from_st_buffer_polygon
----------------------------
(1.5,2.5),(0.5,1.5)
SELECT box(polygon(32, circle('POINT(1 2)'::geometry::point, 0.5::double
precision))::geometry) = box( ST_Buffer('POINT(1 2)'::geometry, 0.5::double
precision)) AS BounderingBoxEquals ;
bounderingboxequals
---------------------
t
=> Have you any explanations on the result (=false) of st_equals (NOT ordering)
and bounderingequals ?
Thanks in advance.
Regards
----- Météo-France -----
PALAYRET JACQUES
DCSC/MBD
jacques.palay...@meteo.fr
Fixe : +33 561078319
