[postgis-devel] OffsetCurve tests

[Sandro Santilli]

Hi Paul, I was reading this commit of yours:

> commit 9b0c432beea50f2b5071a50f6a4e11647c092229
> Author: Paul Ramsey <pramsey at cleverelephant.ca>
> Date:   Tue Jan 4 14:20:01 2022 -0800
> 
>     Revise regression tests so that both pre- and post-GEOS 3.11
>     updates to OffsetCurve will pass.

[...]

> +-- SELECT 't14', ST_AsEWKT(ST_Normalize(ST_OffsetCurve(
> +--  'LINESTRING(0 0,0 20, 10 20, 10 10, 0 10)', -2,
> +--  ''
> +-- )));
> +-- SELECT 't15', ST_AsEWKT(ST_Normalize(ST_OffsetCurve(
> +--  'GEOMETRYCOLLECTION(LINESTRING(0 0,0 20, 10 20, 10 10, 0 10),MULTILINESTRING((2 0,2 20, 12 20, 12 10, 2 10),(3 0,3 20, 13 20, 13 10, 3 10)))', -2,
> +--  ''
> +-- )));

With GEOS 3.11.0dev (unknown hash) from t14 I get the result
which was expected:

  MULTILINESTRING((2 12,8 12,8 18,2 18,2 12),(2 8,2 0))

The new GEOS gives:

  LINESTRING(2 0,2 8)

Shouldn't the new GEOS result be considered bogus instead ?

In the ASCII drawing below, you see the input (with arrow
signs showing the direction) and the previous result of the
offset:

    .--->----.
    | .----, |
    ^ |    | v
    | '----' |
    |---<----'
    |
    ^ |
    | |
    | |

The new result is basically ONLY returning the vertical open
line on the bottom and completely missing the inner rectangle
on top.

--strk;