129 lines
3.6 KiB
PL/PgSQL
129 lines
3.6 KiB
PL/PgSQL
\set ON_ERROR_STOP on
|
|
SET plpgsql.extra_errors TO 'all';
|
|
|
|
drop function if exists detect_bends;
|
|
-- detect_bends detects bends using the inflection angles. It does not do corrections.
|
|
create or replace function detect_bends(line geometry, OUT bends geometry[]) as $$
|
|
declare
|
|
pi real;
|
|
p geometry;
|
|
p1 geometry;
|
|
p2 geometry;
|
|
p3 geometry;
|
|
bend geometry;
|
|
prev_sign int4;
|
|
cur_sign int4;
|
|
begin
|
|
pi = radians(180);
|
|
|
|
-- the last vertex is iterated over twice, because the algorithm uses 3 vertices
|
|
-- to calculate the angle between them.
|
|
--
|
|
-- Given 3 vertices p1, p2, p3:
|
|
--
|
|
-- p1___ ...
|
|
-- /
|
|
-- ... _____/
|
|
-- p3 p2
|
|
--
|
|
-- When looping over the line, p1 will be head (lead) vertex, p2 will be the
|
|
-- measured angle, and p3 will be trailing. The line that will be added to
|
|
-- the bend will always be [p3,p2].
|
|
-- So once the p1 becomes the last vertex, the loop terminates, and the
|
|
-- [p2,p1] line will not have a chance to be added. So the loop adds the last
|
|
-- vertex twice, so it has a chance to become p2, and be added to the bend.
|
|
--
|
|
for p in (
|
|
(select geom from st_dumppoints(line) order by path[1] asc)
|
|
union all
|
|
(select geom from st_dumppoints(line) order by path[1] desc limit 1)
|
|
) loop
|
|
p3 = p2;
|
|
p2 = p1;
|
|
p1 = p;
|
|
if p3 is null then
|
|
continue;
|
|
end if;
|
|
cur_sign = sign(pi - st_angle(p1, p2, p2, p3));
|
|
|
|
if bend is null then
|
|
bend = st_makeline(p3, p2);
|
|
else
|
|
bend = st_linemerge(st_union(bend, st_makeline(p3, p2)));
|
|
end if;
|
|
|
|
if prev_sign + cur_sign = 0 then
|
|
if bend is not null then
|
|
bends = bends || bend;
|
|
end if;
|
|
bend = st_makeline(p3, p2);
|
|
end if;
|
|
prev_sign = cur_sign;
|
|
end loop;
|
|
|
|
-- the last line may be lost if there is no "final" inflection angle. Add it.
|
|
if (select count(1) >= 2 from st_dumppoints(bend)) then
|
|
bends = bends || bend;
|
|
end if;
|
|
end
|
|
$$ language plpgsql;
|
|
|
|
-- fix_gentle_inflections moves bend endpoints following "Gentle Inflection at
|
|
-- End of a Bend" section.
|
|
--
|
|
-- The text does not specify how many vertices can be "adjusted"; it can
|
|
-- equally be one or many. This function is adjusting many, as long as the
|
|
-- commulative inflection angle is less than pi/6 (30 deg).
|
|
create or replace function fix_gentle_inflections(INOUT bends geometry[]) as $$
|
|
declare
|
|
prev_bend geometry;
|
|
bend geometry;
|
|
p geometry;
|
|
p1 geometry;
|
|
p2 geometry;
|
|
p3 geometry;
|
|
begin
|
|
foreach bend in array bends loop
|
|
if prev_bend is null then
|
|
prev_bend = bend;
|
|
continue;
|
|
end if;
|
|
|
|
-- Predicate: two bends will always share an edge. Assuming (A,B,C,D,E,F)
|
|
-- is a bend:
|
|
-- C________D
|
|
-- / \
|
|
-- \________/ \_______/
|
|
-- A B E F
|
|
--
|
|
-- Then edges (A,B) and (E,F) are shared with the neighboring bends.
|
|
--
|
|
--
|
|
-- Assume this curve:
|
|
--
|
|
-- A______B
|
|
-- ---' `---.___. E
|
|
-- C D |
|
|
-- _I |
|
|
-- '---.________ |
|
|
-- H G'---+ F
|
|
--
|
|
-- After processing the curve following the definition of a bend, the bend
|
|
-- [A-G] would be detected. Assuming inflection point G and H are "small",
|
|
-- the bend would be extended by two edges to [A,I].
|
|
for p in (select geom from st_dumppoints(prev_bend) order by path[1] desc) loop
|
|
p3 = p2;
|
|
p2 = p1;
|
|
p1 = p;
|
|
if p3 is null then
|
|
continue;
|
|
end if;
|
|
|
|
-- (p2, p1) is shared with the current bend.
|
|
end loop;
|
|
|
|
prev_bend = bend;
|
|
end loop;
|
|
end
|
|
$$ language plpgsql;
|