Ring geometries in pgRouting OSM DUMP

Question

After performing pgRouting's "pgr_analyzeGraph" algorithm, over an Open Street Map dump uploaded to my PostGIS DB, I get this output, by I can't figure out what "ring geometries" are. Does somebod knows?

NOTICE:  PROCESSING:
NOTICE:  pgr_analyzeGraph(ejes_osm_noded',5,'geom','id','source','target','true')
NOTICE:  Performing checks, please wait ...
NOTICE:  Analyzing for dead ends. Please wait...
NOTICE:  Analyzing for gaps. Please wait...
NOTICE:  Analyzing for isolated edges. Please wait...
NOTICE:  Analyzing for ring geometries. Please wait...
NOTICE:  Analyzing for intersections. Please wait...
NOTICE:              ANALYSIS RESULTS FOR SELECTED EDGES:
NOTICE:                    Isolated segments: 0
NOTICE:                            Dead ends: 16381
NOTICE:  Potential gaps found near dead ends: 265
NOTICE:               Intersections detected: 14412
NOTICE:                      Ring geometries: 20

Total query runtime: 01:23 minutes
1 fila recuperada.

Answer 1

I've made an experiment. Just closed one of the isolated roads.

Before this I got result of pgr_analyzeGraph

NOTICE: Ring geometries: 6

After closing that road I've got

NOTICE: Ring geometries: 7

So the ring geometry is just a closed and isolated linestring.

Answer 2

I believe it is when a segment closes on itself. It occurs when a street is a dead-end with a final "circle". These segments are a bit of a pain as the address parity changes in the middle of the segment. Typically one side has no address, and the other side has addresses 1 to 100 (or whatever) odd + even. Moreover the the max civic number is also at the middle of the segment