Difference between two curvepolygon with same coordinates but not the same order

[MONTICOLO Julien]

Hello everyone,

I find a difference (ST_DIFFERENCE) between two curvepolygons and the only difference is the order of the coordinates.

Bellow my configuration and how to reproduce.

-- configuration
SELECT version() ;  -- PostgreSQL 16.9 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-26), 64-bit
SELECT postgis_version();  -- 3.4 USE_GEOS=1 USE_PROJ=1 USE_STATS=1

-- how to reproduce

I have 4 coordinates A, B, C, D in EPSG=3948, RGF93 / Lambert-93, one of french main CRS zone.
They describe a pseudo-circle (that isn't a perfect circle) : A is the West point, B the North point, C the East point and D the South point.

A = 2039857.003 7263858.968
B = 2039857.799 7263859.772
C = 2039858.603 7263858.976
D = 2039857.807 7263858.172

I have a Curvepolygon ABCDA and a Curvepolygon inner ring ADCBA.
I tried to compute the difference between this two (I converted the inner ring hole into a Curvepolygon but always counterclockwise) :

SELECT
    ST_AREA(
        ST_DIFFERENCE(
            ST_GeomFromEWKT('SRID=3948;
                CURVEPOLYGON(
                    CIRCULARSTRING(
                        2039857.003 7263858.968,  -- A
                        2039857.799 7263859.772,  -- B
                        2039858.603 7263858.976,  -- C
                        2039857.807 7263858.172,  -- D
                        2039857.003 7263858.968   -- A
                    )
                )'
            ),
            ST_GeomFromEWKT('SRID=3948;
                CURVEPOLYGON(
                    CIRCULARSTRING(
                        2039857.003 7263858.968,  -- A
                        2039857.807 7263858.172,  -- D
                        2039858.603 7263858.976,  -- C
                        2039857.799 7263859.772,  -- B
                        2039857.003 7263858.968   -- A
                    )
                )'
            )
        )
    )
;

-- result : 9.023311828629255e-10

I suspected 0.
I reduced the precision to 0 so no flotting point and then the difference gave 0.
I tried to get the difference between the circularstrings, nothing.

I think I missing something. Have you some explanations ?

Thank you in advance,

Best regards,
Julien Monticolo

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