estimate how long the algo will take

IV/tests-integration.sql

@@ -3,6 +3,16 @@
 drop table if exists wm_debug;
 create table wm_debug(stage text, name text, gen bigint, nbend bigint, way geometry, props jsonb);
 
+do $$
+declare
+  npoints bigint;
+  secs bigint;
+begin
+  select * from ST_SimplifyWM_Estimate((select st_union(way) from agg_rivers)) into npoints, secs;
+  raise notice 'Total points: %', npoints;
+  raise notice 'Expected duration: %s (+-%s), depending on bend complexity', ceil(secs), floor(secs*.5);
+end $$ language plpgsql;
+
 drop table if exists wm_demo;
 create table wm_demo (name text, i bigint, way geometry);
 insert into wm_demo (name, way) select name, ST_SimplifyWM(way, name) from agg_rivers;

IV/tests.sql

@@ -56,7 +56,6 @@ insert into wm_figures (name, way) values ('multi-island',ST_GeomFromText('MULTI
 insert into wm_figures (name, way) values ('selfcrossing-1',ST_GeomFromText('LINESTRING(-27 180,-20 166,-21 142,-18 136,55 136,55 136,71 145,44 165,37 146,22 145,14 164,11 164,3 146,-12 146,-13 176,-18 184)'));
 insert into wm_figures (name, way) values ('selfcrossing-1-rev',ST_Reverse(ST_Translate((select way from wm_figures where name='selfcrossing-1'), 0, 60)));
 
-
 -- Run ST_SimplifyWM in debug mode, so `wm_debug` is populated. That table
 -- is used for geometric assertions later in the file.
 drop table if exists wm_demo;

IV/wm.sql

@@ -441,6 +441,33 @@ begin
 end
 $$ language plpgsql;
 
+drop function if exists ST_SimplifyWM_Estimate;
+create function ST_SimplifyWM_Estimate(
+  geom geometry,
+  OUT npoints bigint,
+  OUT secs bigint
+) as $$
+declare
+  lines geometry[];
+  l_type text;
+begin
+  l_type = st_geometrytype(geom);
+  if l_type = 'ST_LineString' then
+    lines = array[geom];
+  elseif l_type = 'ST_MultiLineString' then
+    lines = array((select a.geom from st_dump(geom) a order by path[1] asc));
+  else
+    raise 'Unknown geometry type %', l_type;
+  end if;
+
+  npoints = 0;
+  for i in 1..array_length(lines, 1) loop
+    npoints = npoints + st_numpoints(lines[i]);
+  end loop;
+  secs = npoints / 800;
+end
+$$ language plpgsql;
+
 -- ST_SimplifyWM simplifies a given geometry using Wang & Müller's
 -- "Line Generalization Based on Analysis of Shape Characteristics" algorithm,
 -- 1998.