/*
Function to create a line based on dynamic segmentation. 
INPUT: linestring to segmentate,
       startpoint in percent of line (0..1)
			 endpoint in percent of line (0..1)
			 
OUTPUT: dynseg linestring 			 
			 
Dr. Horst Düster, Solothurn 5.5.2004			 
*/

CREATE OR REPLACE FUNCTION dynseg (GEOMETRY, DOUBLE PRECISION,DOUBLE PRECISION) RETURNS GEOMETRY AS '

DECLARE
  theLine ALIAS FOR $1;
  fmeas ALIAS FOR $2;
  tmeas ALIAS FOR $3;
  npoints INTEGER;
	fuzzy double precision := 0.1;
  start_pnt GEOMETRY;
  end_pnt GEOMETRY;
  lineSeg GEOMETRY;
  tempLineString GEOMETRY;
  result_geom GEOMETRY;
	test GEOMETRY;
  test_start BOOLEAN := ''f'';
  test_end BOOLEAN := ''f'';
  first BOOLEAN := ''t'';
	last BOOLEAN := ''f'';

BEGIN

-- Identify the number of vertex points
  SELECT numpoints(theLine) INTO npoints;
	
-- Identify the coordinates of start- and endpoint	
  start_pnt := line_interpolate_point(theLine,fmeas);
  end_pnt := line_interpolate_point(theLine,tmeas);

-- generate the first linesegment 	
  tempLineString := geomfromtext(''LINESTRING(''|| x(pointn(theLine,1))||'' ''||y(pointn(theLine,1))||'',''||x(pointn(theLine,2))||'' ''||y(pointn(theLine,2))||'')'',srid(theLine));

-- test if start- or/and endpoint touching the linesegment	
	SELECT distance(start_pnt,tempLineString) < fuzzy INTO test_start;
  SELECT distance(end_test,tempLineString) < fuzzy INTO test_end;			
	
-- do for all other linesegments	
  FOR i IN 2..npoints LOOP
	
-- if startpoint is touching the linesegment begin aggregate all following linesegments to the 
-- dynseg line until linesegment touching endpoint is reached
    IF test_start AND first THEN 
		  result_geom := geomfromtext(''LINESTRING(''|| x(start_pnt)||'' ''||y(start_pnt)||'',''||x(pointn(tempLineString,2))||'' ''||y(pointn(tempLineString,2))||'')'',srid(tempLineString));			
			first := ''f'';			
	    tempLineString := geomfromtext(''LINESTRING(''|| x(pointn(theLine,i))||'' ''||y(pointn(theLine,i))||'',''||x(pointn(theLine,i+1))||'' ''||y(pointn(theLine,i+1))||'')'',srid(theLine));
  		SELECT intersects(end_test,tempLineString) INTO test_end;			
		ELSIF not test_end AND test_start THEN 
	    result_geom := geomunion(result_geom,tempLineString);			
  	  tempLineString := geomfromtext(''LINESTRING(''|| x(pointn(theLine,i))||'' ''||y(pointn(theLine,i))||'',''||x(pointn(theLine,i+1))||'' ''||y(pointn(theLine,i+1))||'')'',srid(theLine));
      SELECT intersects(end_test,tempLineString) INTO test_end;
		ELSIF not last AND test_end AND test_start THEN
			result_geom := geomunion(result_geom,tempLineString);
  	  tempLineString := geomfromtext(''LINESTRING(''|| x(pointn(theLine,i))||'' ''||y(pointn(theLine,i))||'',''||x(end_pnt)||'' ''||y(end_pnt)||'')'',srid(theLine));
			result_geom := geomunion(result_geom,tempLineString);
			last := ''t'';													  
  	ELSE		
  	  tempLineString := geomfromtext(''LINESTRING(''|| x(pointn(theLine,i))||'' ''||y(pointn(theLine,i))||'',''||x(pointn(theLine,i+1))||'' ''||y(pointn(theLine,i+1))||'')'',srid(theLine));
	  	SELECT intersects(start_test,tempLineString) INTO test_start;			
		END IF;
	END LOOP;
  RETURN result_geom;
END;
' LANGUAGE plpgsql;