Hi L.
I would suspect the first assignment of the result_pnt (result_pnt :=
ST_Collect(result_pnt, st_pointn(lineusp, point_id));) as the cause of
the problem: Within your assignment, you try to use the geometry of
result_pnt which does not yet exist at this moment. Maybe, you could
work with an IF clause to assign some sort of start value to your
result_pnt variable.
Regards,
Birgit.
Am 11.06.2014 10:56, schrieb Pier Lorenzo Marasco:
I tried to modify spikeRemover from Schmidt & Krüger to obtain just
the spike position. For some reason, that I can't figure out, my
script fails and I don't obtain a multipoint position. Probably there
is a problem in the aggregation of different points but I don't know
how to manage it in another way. I tried with ST_collect and ST_union
but with both I don't obtain a right geometry.
CREATE OR REPLACE FUNCTION ST_SpikeFinder (geometry, angle double
precision)
returns geometry as
$body$
DECLARE
ingeom alias for $1;
angle alias for $2;
lineusp geometry;
newgeom geometry;
numpoints integer;
point_id integer;
result_pnt geometry;
begin
-- input geometry or rather set as default for the output
newgeom := ingeom;
-- check polygon
if (select st_geometrytype(ingeom)) = 'ST_Polygon' then
if (select st_numinteriorrings(ingeom)) = 0 then
lineusp := st_boundary(ingeom) as line;
numpoints := st_numpoints(lineusp);
point_id := 0;
-- the geometry passes pointwisely
while (point_id <= numpoints) loop
result_pnt := ST_Collect(result_pnt,
st_pointn(lineusp, point_id));
-- the check of the angle at the current point of
a spike including the special case, that it is the first point.
if (select abs(pi() -
abs(st_azimuth(st_pointn(lineusp, case when point_id= 1 then
st_numpoints(lineusp) - 1 else point_id - 1 end),
st_pointn(lineusp, point_id)) -
st_azimuth(st_pointn(lineusp, point_id), st_pointn(lineusp, point_id +
1))))) <= angle then
(probably the problem is here) ---> result_pnt :=
ST_Union(result_pnt, st_pointn(lineusp, point_id));
end if;
point_id = point_id + 1;
end loop;
end if;
end if;
return result_pnt;
end;
$body$
language 'plpgsql' volatile;
Any idea ?
Thank you in advance.
L.
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