[postgis-users] Create LINESTRING with a LOOP

[paallen at attglobal.net]

Mark,

Thanks for your suggestion.  After pouring over
the documentation more I gave up on starting with
a null linestring and just put a IF THEN in to
check for the 1st & 2nd points.  Below was my fix.

But actually I started off using a large text
string, then feeding it into the EWKT all at once
and that is where I ran into problems.  Which is
why I then tried to build up the line using
geometries incrementally.

This script was just a really simplified example
of what I need to do.  My real function is looping
through a series of records (<100-200) containing
distances &  orientations along a curved line and
calculating coordinates for a from/to (begin/end)
distance (using Minimum Curvature Alogrithm that I
have written in pl/pgsql).  And it appears that
for really long LINESTRINGS it craps out.  If I
run the function returning just a  text string of
the coordinates, the coordinates look fine.  But
when I convert them to a LINESTRING it returns
nothing.  If I reduce the length, or number of
nodes, it works.

So now the question is, "Is there a limit to the
number of nodes in a LINESTRING?" ?  

I cannot believe so but it is the only solution
that I can think of.

Phil


CREATE OR REPLACE FUNCTION mc_test2( )
	RETURNS geometry AS
$BODY$
	DECLARE
		gline geometry;
		gpt geometry;
		x integer;
		str text;
		str1 text;
	BEGIN
	x := 1;
		WHILE (x <= 5) LOOP
			str := $$SRID=32717;POINT($$ || 400000 + x ||
$$ $$ || 900000 + x || $$ $$ || 3500 + x || $$ $$
|| x || $$)$$;
			IF (x > 2) THEN
				gline := AddPoint(gline, GeomFromEWKT(str));
			ELSIF (x=1) THEN
				str1 := str;
			ELSIF (x=2) THEN
				gline := MakeLine(GeomFromEWKT(str1),
GeomFromEWKT(str) );
			END IF;

			x := x+1;

		END LOOP;

		RETURN gline;
	END;
$BODY$
  LANGUAGE 'plpgsql' VOLATILE;