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move section of self_crossing to a separate function

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Motiejus Jakštys 2021-05-19 22:57:47 +03:00 committed by Motiejus Jakštys
parent fd1250a73b
commit 5491f574e6
1 changed files with 39 additions and 26 deletions
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65
wm.sql
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@ -209,6 +209,34 @@ begin
end
$$ language plpgsql;
drop function if exists if_selfcross;
create function if_selfcross(
bendi geometry,
bendj geometry
) returns geometry as $$
declare
a geometry;
b geometry;
partitions geometry;
begin
a = st_pointn(bendi, 1);
b = st_pointn(bendi, -1);
partitions = st_split(bendj, st_makeline(a, b));
if st_numgeometries(partitions) = 1 then
return null;
end if;
if st_numgeometries(partitions) = 2 and
(st_contains(bendj, a) or st_contains(bendj, b)) then
return null;
end if;
return partitions;
end
$$ language plpgsql;
-- self_crossing eliminates self-crossing from the bends, following the
-- article's section "Self-line Crossing When Cutting a Bend".
drop function if exists self_crossing;
@ -220,7 +248,6 @@ declare
pi constant real default radians(180);
i int4;
j int4;
prev_length int4;
a geometry;
b geometry;
multi geometry;
@ -234,25 +261,18 @@ begin
-- self-crossing. now try to find another bend in this line that
-- crosses an imaginary line of end-vertices
-- To understand the block below, I suggest you take a pencil and paper,
-- draw a self-crossing bend (fig6 from the article works well), and
-- figure out what happens here, by hand. I know it's hard to follow.
-- Apologies.
-- go through each bend in the given line, and see if has a potential to
-- cross bends[i].
for j in 1..i-1 loop
a = st_pointn(bends[i], 1);
b = st_pointn(bends[i], -1);
multi = st_split(bends[j], st_makeline(a, b));
continue when st_numgeometries(multi) = 1;
continue when st_numgeometries(multi) = 2 and
(st_contains(bends[j], a) or st_contains(bends[j], b));
-- vertices, segments and stars are aligned, we are changing the bend
select if_selfcross(bends[i], bends[j]) into multi;
continue when multi is null;
mutated = true;
-- To understand the block below, I suggest you take a pencil and paper,
-- draw a self-crossing bend (fig6 from the article works well), and
-- figure out what happens here, by hand. I know it's hard to follow.
-- Apologies.
prev_length = array_length(bends, 1);
-- remove first vertex of the following bend, because the last
-- segment is always duplicated with the i'th bend.
bends[i+1] = st_removepoint(bends[i+1], 0);
@ -262,26 +282,19 @@ begin
st_npoints(bends[j])-1,
st_pointn(bends[i], st_npoints(bends[i]))
);
bends = bends[1:j] || bends[i+1:prev_length];
bends = bends[1:j] || bends[i+1:];
exit;
end loop;
for j in reverse array_length(bends, 1)..i+1 loop
a = st_pointn(bends[i], 1);
b = st_pointn(bends[i], -1);
multi = st_split(bends[j], st_makeline(a, b));
continue when st_numgeometries(multi) = 1;
continue when st_numgeometries(multi) = 2 and
(st_contains(bends[j], a) or st_contains(bends[j], b));
-- vertices, segments and stars are aligned, we are changing the bend
select if_selfcross(bends[i], bends[j]) into multi;
continue when multi is null;
mutated = true;
-- To understand the block below, I suggest you take a pencil and paper,
-- draw a self-crossing bend (fig6 from the article works well), and
-- figure out what happens here, by hand. I know it's hard to follow.
-- Apologies.
prev_length = array_length(bends, 1);
-- remove last vertex of the previous bend, because the last
-- segment is duplicated with the i'th bend.
bends[i-1] = st_removepoint(bends[i-1], st_npoints(bends[i-1])-1);
@ -290,7 +303,7 @@ begin
st_pointn(bends[i], 1),
st_removepoint(st_geometryn(multi, st_numgeometries(multi)), 0)
);
bends = bends[1:i] || bends[j+1:prev_length];
bends = bends[1:i] || bends[j+1:];
exit;
end loop;
end loop;