Circles with circle() vs ST_Buffer() Equality equalities

[PALAYRET Jacques <jacques.palayret@xxxxxxxx>]

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.palayret@xxxxxxxx
Fixe : +33 561078319