44 lines
987 B
PL/PgSQL
44 lines
987 B
PL/PgSQL
\set ON_ERROR_STOP on
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SET plpgsql.extra_errors TO 'all';
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create or replace function detect_bends(line geometry) returns table(bend geometry) as $$
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/* for each bend, should return:
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- size (area)
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- shape (cmp, compactness index)
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*/
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declare
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pi real;
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p geometry;
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p1 geometry;
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p2 geometry;
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p3 geometry;
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prev_sign int4;
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cur_sign int4;
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begin
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pi = radians(180);
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for p in (select (dp).geom from st_dumppoints(line) as dp) loop
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p3 = p2;
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p2 = p1;
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p1 = p;
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if p3 is null then
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continue;
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end if;
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cur_sign = sign(pi - st_angle(p1, p2, p2, p3));
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bend = st_linemerge(st_union(bend, st_makeline(p3, p2)));
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if prev_sign + cur_sign = 0 then
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if bend is not null then
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return next;
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end if;
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bend = st_makeline(p3, p2);
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end if;
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prev_sign = cur_sign;
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end loop;
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end
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$$ language plpgsql;
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drop table if exists bends;
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create table bends as (select * from detect_bends((select way from figures where name='fig3')));
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