bend detection

bend.sql

@@ -1,3 +1,6 @@
+\set ON_ERROR_STOP on
+SET plpgsql.extra_errors TO 'all';
+
 create or replace function detect_bends(line geometry) returns table(bend geometry) as $$
 /* for each bend, should return:
    - size (area)
@@ -9,6 +12,8 @@ declare
   p1 geometry;
   p2 geometry;
   p3 geometry;
+  prev_sign int4;
+  cur_sign int4;
 begin
   pi = radians(180);
 
@@ -16,8 +21,20 @@ begin
     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));
+    if p3 is null then
+      continue;
+    end if;
+    cur_sign = sign(pi - st_angle(p1, p2, p2, p3));
+
+    bend = st_linemerge(st_union(bend, st_makeline(p3, p2)));
+
+    if prev_sign + cur_sign = 0 then
+      if bend is not null then
+        return next;
+      end if;
+      bend = st_makeline(p3, p2);
+    end if;
+    prev_sign = cur_sign;
   end loop;
 end
 $$ language plpgsql;