simplify_error.py

#! /usr/bin/python3

import shapely.wkt
import shapely.wkb
import shapely.geometry
import psycopg2

s= open('121897178.wkt').read()
sh= shapely.wkt.loads(s)

conn= psycopg2.connect(dbname='gis')
cur= conn.cursor()

nodes= list (sh.exterior.coords)
count= len (nodes)
i= 0

while True:
    # make a copy, remove element i, keep Polygon closed
    new_nodes= nodes[:]
    print (nodes[:20], i)
    new_nodes.pop (i)
    if i==0:
        new_nodes[-1]= new_nodes[0]

    shape= shapely.geometry.Polygon(new_nodes)

    if not shape.is_valid:
        i+= 1
        continue

    try:
        cur.execute ('select ST_StraightSkeleton(%s);', (shapely.wkb.dumps(shape),))

        # the Polygon is ok, so i is problematic
        # keep it
        i+= 1

    except psycopg2.InternalError as e:
        print (e)

        # the Polygon is not ok, so remove i
        nodes= new_nodes
        # we reached the end of the line
        # -2 because we need at least 3 points (orig, other, orig) to make a Polygon
        if i==len (nodes)-2:
            break

        # the cursor is no longer valid, reopen
        cur.close()
        conn.rollback()
        cur= conn.cursor()

print (shapely.wkt.dumps (shape))