PLPGSQL Function to cross the dateline

AXH_CrossDateLine.sql

--
-- Create a valid GEOMETRY in 3857 like the_geom_webmercator
--
-- @param pointa is GEOMETRY in 3857 like the_geom_webmercator
--
-- @param pointb is GEOMETRY in 3857 like the_geom_webmercator
--  
--

CREATE OR REPLACE FUNCTION AXH_CrossDateLine (pointa GEOMETRY, pointb GEOMETRY) RETURNS geometry as $$ 
DECLARE
  westmost GEOMETRY; 
  eastmost GEOMETRY; 
  h FLOAT8;
  p FLOAT8;
  zy FLOAT8;
BEGIN 
	IF ST_SRID(pointa) != 3857 THEN 
		pointa = ST_Transform(pointa, 3857);
	END IF;
	IF ST_SRID(pointb) != 3857 THEN 
		pointb = ST_Transform(pointb, 3857);
	END IF;

	IF ST_X(pointa) < ST_X(pointb) THEN
		westmost := pointa;
		eastmost := pointb;
	ELSE
		westmost := pointb;
		eastmost := pointa;
	END IF;

	h := GREATEST(ST_Y(eastmost), ST_Y(westmost)) - LEAST(ST_Y(eastmost), ST_Y(westmost));

	p := (h / (20037508.34 - ST_X(eastmost) + ST_X(westmost) + 20037508.34 )) * (20037508.34 - ST_X(eastmost));

	zy := LEAST(ST_Y(eastmost), ST_Y(westmost)) + p;

    RETURN ST_Collect(
    	ST_MakeLine(eastmost, ST_SetSRID(ST_MakePoint(20037508.34, zy),3857)),
    	ST_MakeLine(ST_SetSRID(ST_MakePoint(-20037508.34, zy),3857), westmost)
    );
END; 
$$ language plpgsql IMMUTABLE;

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