Paths can be circular

[justinefricou]

Paths should not be circular, but existing constraints do not actually ensure it:

Geotrek-admin/geotrek/core/templates/core/sql/post_40_paths.sql

Lines 89 to 90 in 7b7e045

	ALTER TABLE core_path ADD CONSTRAINT core_path_geom_isvalid CHECK (ST_IsValid(geom));
	ALTER TABLE core_path ADD CONSTRAINT core_path_geom_issimple CHECK (ST_IsSimple(geom));

Example: 'SRID=2154;LINESTRING (220720.2970061041 6839647.216621559, 220754.7791213283 6839679.476219036, 220784.1131707298 6839651.675301611,220720.2970061041 6839647.216621559)'

SELECT ST_IsValid(ST_GeomFromText('SRID=2154;LINESTRING (220720.2970061041 6839647.216621559, 220754.7791213283 6839679.476219036, 220784.1131707298 6839651.675301611,220720.2970061041 6839647.216621559)'));
 st_isvalid 
------------
 t
(1 row)

SELECT ST_IsSimple(ST_GeomFromText('SRID=2154;LINESTRING (220720.2970061041 6839647.216621559, 220754.7791213283 6839679.476219036, 220784.1131707298 6839651.675301611,220720.2970061041 6839647.216621559)'));
 st_issimple 
-------------
 t
(1 row)

Some factors that need to be considered:

• what implications will path snapping have on this?
• currently, the merge_segmented_paths command can merge two paths into a circular one if both of their extremities touch
• users will need to split any circular paths in their databases prior to updating to a version that introduces this change