[postgis-devel] ST_Normalize issues (was ST_Reverse issues)

[Sandro Santilli]

So it looks like ST_Normalize sometimes changes winding order
of closed linestrings to be CW and sometimes changes them to be CCW

Here's an example:

  WITH inp AS (
    SELECT 't1' lbl, 'LINESTRING(0 0,10 0,5 5,0 0)'::geometry g
    UNION ALL
    SELECT 't3', 'LINESTRING(0 0,-10 0,-5 -5,0 0)'::geometry
  ),
  back_and_forw AS (
    SELECT lbl, g, st_reverse(g) rg from inp
  )
  SELECT
    -- We expect both fields being true
    lbl,
      ST_AsText(g) forw,
      ST_AsText(rg) back,
      ST_AsText(ST_Normalize(g)) norm_forw,
      ST_AsText(ST_Normalize(rg)) norm_back,
      ST_IsPolygonCW(ST_MakePolygon(g)) forw_cw,
      ST_IsPolygonCW(ST_MakePolygon(rg)) back_cw,
      ST_IsPolygonCW(ST_MakePolygon(ST_Normalize(g))) norm_forw_cw,
      ST_IsPolygonCW(ST_MakePolygon(ST_Normalize(rg))) norm_back_cw
  FROM back_and_forw;

The result:


    -[ RECORD 1 ]+--------------------------------
    lbl          | t1
    forw         | LINESTRING(0 0,10 0,5 5,0 0)
    back         | LINESTRING(0 0,5 5,10 0,0 0)
    norm_forw    | LINESTRING(0 0,5 5,10 0,0 0) 
    norm_back    | LINESTRING(0 0,5 5,10 0,0 0)
    forw_cw      | f
    back_cw      | t
    norm_forw_cw | t
    norm_back_cw | t
    -[ RECORD 2 ]+--------------------------------
    lbl          | t3
    forw         | LINESTRING(0 0,-10 0,-5 -5,0 0)
    back         | LINESTRING(0 0,-5 -5,-10 0,0 0)
    norm_forw    | LINESTRING(0 0,-10 0,-5 -5,0 0)
    norm_back    | LINESTRING(0 0,-10 0,-5 -5,0 0)
    forw_cw      | f
    back_cw      | t
    norm_forw_cw | f
    norm_back_cw | f


The above was obtained with:

  POSTGIS="3.1.2dev 3.1.1-38-gb02ee9513"
  PGSQL="120"
  GEOS="3.8.2dev-CAPI-1.13.4"
  PROJ="7.1.0"
  LIBXML="2.9.10"
  LIBJSON="0.15"
  LIBPROTOBUF="1.3.3"

Does it ring any bell to anyone of you ? Or I guess I'll file a
ticket.

--strk;