IV: finding bends

bend.sql

@@ -0,0 +1,26 @@
+create or replace function detect_bends(line geometry) returns table(bend geometry) as $$
+/* for each bend, should return:
+   - size (area)
+   - shape (cmp, compactness index)
+*/
+declare
+  pi real;
+  p geometry;
+  p1 geometry;
+  p2 geometry;
+  p3 geometry;
+begin
+  pi = radians(180);
+
+  for p in (select (dp).geom from st_dumppoints(line) as dp) loop
+    p3 = p2;
+    p2 = p1;
+    p1 = p;
+    if p3 is null then continue; end if;
+    raise notice 'ANGLE %', degrees(pi - st_angle(p1, p2, p2, p3));
+  end loop;
+end
+$$ language plpgsql;
+
+drop table if exists bends;
+create table bends as (select * from detect_bends((select way from figures where name='fig3')));

db

@@ -0,0 +1,51 @@
+#!/bin/bash
+set -euo pipefail
+
+name=wm-mj
+
+_psql() {
+    env \
+        PGPASSWORD=osm \
+        PGHOST=127.0.0.1 \
+        PGUSER=osm \
+        PGDATABASE=osm \
+        psql "$@"
+}
+
+_wait_for_postgres() {
+    >&2 echo -n "Waiting for postgres"
+    for _ in $(seq 240); do
+      if _psql -qc '\q' 2>/dev/null; then
+          >&2 echo " up"
+          exit 0
+      fi
+      >&2 echo -n .
+      sleep 1
+    done
+    >&2 echo " down"
+    exit 1
+}
+
+case ${1:-} in
+    start)
+        docker run -d --rm \
+            -p 5432:5432 \
+            -e POSTGRES_DBNAME=osm \
+            -e POSTGRES_USER=osm \
+            -e POSTGRES_PASSWORD=osm \
+            --name "$name" \
+            postgis/postgis:13-3.1-alpine
+        _wait_for_postgres
+        ;;
+    stop)
+        docker stop "$name"
+        ;;
+    "" | --)
+        [[ $# -gt 1 ]] && shift
+        _psql "$@"
+        ;;
+    *)
+        >&2 echo "Unknown command: '$*'"
+        exit 1
+        ;;
+esac

figures.sql

@@ -0,0 +1,4 @@
+drop table if exists figures;
+create table figures (name text, way geometry);
+
+insert into figures (name, way) values ('fig3', ST_GeomFromText('LINESTRING(0 0, 12 0, 13 4, 20 2, 20 0, 32 0, 33 10, 38 16, 43 15, 44 10, 44 0, 60 0)'));