(sorry, sent to fast...)
with pg_pts_oriented as (
-- extract exterior ring points
select st_dumpPoints(
-- extract polygon's exterior as a linestring
st_exteriorRing(
-- force polygon orientation
st_forceRHR(
'POLYGON (( 355 215, 390 220, 403 258, 364 234, 375
277, 326 274, 286 243, 355 215 ))'::geometry
)
)
) as d
)
select (p1.d).path[1] as edge_number,
st_makeLine((p1.d).geom, (p2.d).geom) as edge
from pg_pts_oriented p1,
pg_pts_oriented p2
where (p2.d).path[1] = (p1.d).path[1] + 1;You can then play with edge_number to shift it according to choosen vertex index. Nicolas
<<attachment: Screen shot 2012-08-24 at 10.49.09 AM.png>>
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