<font size=2 face="sans-serif">Thanks for the code Simon. After a few
tweaks I got it working perfectly in PostGIS2.</font><br><br><font size=2 face="sans-serif">Here's the updated code.</font><br><br><font size=2 face="sans-serif">Adrian</font><br><br><font size=2 face="sans-serif">CREATE OR REPLACE FUNCTION ST_Extend(eje_
geometry, bound_ geometry)</font><br><font size=2 face="sans-serif">RETURNS geometry</font><br><font size=2 face="sans-serif">AS $$</font><br><font size=2 face="sans-serif">-- Use Case: I need to "extend"
a linestring in another one. The new linestring must be</font><br><font size=2 face="sans-serif">-- obtained such as their new extremes
are the intersection of it with a</font><br><font size=2 face="sans-serif">-- polygon that contains it. The original
linestring is composed of only a</font><br><font size=2 face="sans-serif">-- linear segment.</font><br><font size=2 face="sans-serif">-- version: alfa , by Julio A. Galindo,
April 17, 2007: juliogalindoq at gmail.com</font><br><font size=2 face="sans-serif">DECLARE</font><br><font size=2 face="sans-serif"> b_ geometry = st_boundary(bound_);</font><br><font size=2 face="sans-serif"> dist float;</font><br><font size=2 face="sans-serif"> max_dist float
= 0;</font><br><font size=2 face="sans-serif"> n_points int;</font><br><font size=2 face="sans-serif"> pto_1 geometry;</font><br><font size=2 face="sans-serif"> pto_2 geometry;</font><br><font size=2 face="sans-serif"> first_pto geometry;</font><br><font size=2 face="sans-serif"> last_pto geometry;</font><br><font size=2 face="sans-serif"> u_1 float;</font><br><font size=2 face="sans-serif"> u_2 float;</font><br><font size=2 face="sans-serif"> norm float;</font><br><font size=2 face="sans-serif"> result text = 'LINESTRING(';</font><br><font size=2 face="sans-serif">BEGIN</font><br><font size=2 face="sans-serif"> IF st_GeometryType(eje_)
NOT LIKE 'ST_LineString' OR</font><br><font size=2 face="sans-serif"> st_GeometryType(bound_)
NOT LIKE 'ST_Polygon' THEN</font><br><font size=2 face="sans-serif"> RETURN
NULL;</font><br><font size=2 face="sans-serif"> END IF;</font><br><font size=2 face="sans-serif"> -- First Search
how far is the boundary: (worst case)</font><br><font size=2 face="sans-serif"> pto_1 := st_StartPoint(eje_);</font><br><font size=2 face="sans-serif"> pto_2 := st_EndPoint(eje_);</font><br><font size=2 face="sans-serif"> FOR i IN 1..st_NumPoints(b_)-1
LOOP</font><br><font size=2 face="sans-serif"> dist
:= st_distance(st_PointN(b_,i),pto_1);</font><br><font size=2 face="sans-serif"> IF
dist > max_dist THEN max_dist := dist; --END IF;</font><br><font size=2 face="sans-serif">
max_dist := dist;</font><br><font size=2 face="sans-serif"> END
IF;</font><br><font size=2 face="sans-serif"> dist
:= st_distance(st_PointN(b_,i),pto_2);</font><br><font size=2 face="sans-serif"> IF
dist > max_dist THEN max_dist := dist; --END IF;</font><br><font size=2 face="sans-serif">
max_dist := dist;</font><br><font size=2 face="sans-serif"> END
IF;</font><br><font size=2 face="sans-serif"> END LOOP;</font><br><font size=2 face="sans-serif"> -- Now extent the
linestring:</font><br><font size=2 face="sans-serif"> pto_2 := st_PointN(eje_,2);</font><br><font size=2 face="sans-serif"> u_1 := st_X(pto_2)-st_X(pto_1);</font><br><font size=2 face="sans-serif"> u_2 := st_Y(pto_2)-st_Y(pto_1);</font><br><font size=2 face="sans-serif"> norm := sqrt(u_1^2
+ u_2^2);</font><br><font size=2 face="sans-serif"> first_pto := st_MakePoint(st_X(pto_1)-u_1/norm*dist,st_Y(pto_1)-u_2/norm*dist);</font><br><font size=2 face="sans-serif"> n_points := st_nPoints(eje_);</font><br><font size=2 face="sans-serif"> IF n_points >
2 THEN</font><br><font size=2 face="sans-serif"> pto_1
:= st_PointN(eje_,n_points-1);</font><br><font size=2 face="sans-serif"> pto_2
:= st_PointN(eje_,n_points);</font><br><font size=2 face="sans-serif"> u_1
:= st_X(pto_2)-st_X(pto_1);</font><br><font size=2 face="sans-serif"> u_2
:= st_Y(pto_2)-st_Y(pto_1);</font><br><font size=2 face="sans-serif"> norm
:= sqrt(u_1^2 + u_2^2);</font><br><font size=2 face="sans-serif"> END IF;</font><br><font size=2 face="sans-serif"> last_pto := st_MakePoint(st_X(pto_2)+u_1/norm*dist,st_Y(pto_2)+u_2/norm*dist);</font><br><font size=2 face="sans-serif"> result :=
result || st_X(first_pto) || ' ' || st_Y(first_pto) || ',';</font><br><font size=2 face="sans-serif"> FOR i IN 1..st_NumPoints(eje_)
LOOP</font><br><font size=2 face="sans-serif"> result
:= result || st_X(st_PointN(eje_,i)) || ' ' || st_Y(st_PointN(eje_,i))
|| ',';</font><br><font size=2 face="sans-serif"> END LOOP;</font><br><font size=2 face="sans-serif"> result := result
|| st_X(last_pto) || ' ' || st_Y(last_pto) || ')';</font><br><font size=2 face="sans-serif"> -- Find the final
Linestring:</font><br><font size=2 face="sans-serif"> b_ := st_intersection(st_GeomFromText(result,st_SRID(eje_)),bound_);</font><br><font size=2 face="sans-serif"> RETURN b_;</font><br><font size=2 face="sans-serif"> END $$</font><br><font size=2 face="sans-serif"> LANGUAGE plpgsql</font><br><font size=2 face="sans-serif"> STABLE</font><br><font size=2 face="sans-serif"> RETURNS NULL ON NULL INPUT;</font><br><font size=3><br></font><font size=1 face="Verdana"><br></font><BR>
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