Snapping a polygon (= (to-)snappoly) to a reference polygon (refpoly)

Snap_polygons_to_polygons.sql

/* 
Snapping a polygon (= (to-)snappoly) to a reference polygon (refpoly). 
Note that snapping only works on nearby points of two polygons. 
So there are maybe orphaned points on snappoly which still are nearby 
a refpoly segment but did not snap in the first round. So, in addition 
the closest points on refpoly to the orphaned snappoly points are 
collected and the first snapped poly output is snapped again given 
this closest points collection.
*/
with 
refpoly(gid, geom) as (
  select 1, ST_GeomFromText('POLYGON ((4 1, 4 8, 2 7, 2 3, 4 1))')
), 
snappoly(gid, geom) as (
  select 11, ST_GeomFromText('POLYGON ((6 2, 6 4, 6 6, 7 8, 9 8, 9 3, 6 2))')
),
snappedpoly(gid, geom) as (
  select
    snappoly.gid+100 as gid,
    ST_Snap(snappoly.geom, refpoly.geom, 2.5) as geom
  from 
    snappoly, 
    refpoly
)
select
  c.gid,
  ST_AsText(ST_Snap(c.geom, d.geom, 2.5)) as snapped_geom_fixed,
  ST_AsText(c.geom) as snapped_geom
from 
  snappedpoly c,
  (select 
     ST_Collect(geom) as geom 
   from (
    select 
      ST_ClosestPoint(a.geom, b.geom) as geom
    from 
      refpoly a,
      (select (ST_DumpPoints(geom)).geom as geom from snappedpoly) b
    where ST_Distance(b.geom, a.geom)>0 and ST_Distance(b.geom, a.geom)<2.5 ) tmp
   ) d;