Cannot create Polygon from Points pgr_pointsaspolygon()

[Stophface]

I want to calculate catchment areas. Doing that, I splitted up my process into two functions.
The first functions identifies the points which can be reached in time. With the second function I want to create polygons, based on driving time.

CREATE OR REPLACE FUNCTION nodes(lon numeric, lat numeric, time integer)
RETURNS void AS
$$

CREATE table nodes_tab AS
SELECT dd.seq, dd.node, dd.cost, dd.agg_cost,
ST_SetSRID(
	ST_Point(
		ST_X(wvp.the_geom), 
		ST_Y(wvp.the_geom)), 4326
	) as the_geom
FROM pgr_drivingdistance('
	SELECT gid AS id,
		source,
		target,
		CASE 
		WHEN some_f(a) = -1.0 
		THEN -1.0 
		ELSE cost_s END 
		AS cost,
	reverse_cost_s AS reverse_cost
	FROM ways',
	pgr_pointToEdgeNode('ways', ST_SetSRID(
		ST_Point($1, $2), 
		4326), 0.01
	),
	$3, 
	directed := true) AS dd INNER JOIN 
		ways_vertices_pgr 
		AS wvp 
		ON dd.node = wvp.id;
$$ 
language 'sql';

The created table is correct.
Then I want to create polygons, based on the points.
Doing that I use the pointsaspolygons function http://docs.pgrouting.org/latest/en/src/alpha_shape/doc/pgr_pointsAsPolygon.html#pgr-points-as-polygon

SELECT pgr_pointsAsPolygon( 
		'cnt.seq AS id, 
		ST_X(cnt.the_geom) AS x, 
		ST_Y(cnt.the_geom) AS y')
		FROM nodes_tab cnt;

That throws me an error I do not even understand:

ERROR: syntax error at or near "cnt"
LINE 1: cnt.seq AS id,
^
QUERY: cnt.seq AS id,
ST_X(cnt.the_geom) AS x,
ST_Y(cnt.the_geom) AS y
CONTEXT: PL/pgSQL function pgr_pointsaspolygon(character varying,double precision) line 17 at FOR over EXECUTE statement
********** Error **********

ERROR: syntax error at or near "cnt"
SQL state: 42601
Context: PL/pgSQL function pgr_pointsaspolygon(character varying,double precision) line 17 at FOR over EXECUTE statement

At the first glance one could think that this is related to this error:
http://gis.stackexchange.com/questions/215203/cannot-create-pgr-pointsaspolygon-from-pgr-drivingdistance-function/215218#215218

However, I am not using a nested query with quotes...
Note: I asked here as well if this behaviour is known: http://gis.stackexchange.com/questions/221794/cannot-create-polygon-from-points

[cvvergara]

from your query::

SELECT pgr_pointsAsPolygon( 
		'cnt.seq AS id, 
		ST_X(cnt.the_geom) AS x, 
		ST_Y(cnt.the_geom) AS y')
		FROM nodes_tab cnt;

the inner SQL query is:

                 cnt.seq AS id, 
		ST_X(cnt.the_geom) AS x, 
		ST_Y(cnt.the_geom) AS y

but the real query is

SELECT cnt.seq AS id,  
		ST_X(cnt.the_geom) AS x, 
		ST_Y(cnt.the_geom) AS y
		FROM nodes_tab cnt

this last query is the one that should be used as inner query

rewriting:

SELECT pgr_pointsAsPolygon( 
		'SELECT cnt.seq AS id,  
		ST_X(cnt.the_geom) AS x, 
		ST_Y(cnt.the_geom) AS y
		FROM nodes_tab cnt'
);

p.d. you are using

pgr_pointToEdgeNode('ways', ST_SetSRID(
		ST_Point($1, $2), 
		4326), 0.01
	),

Which is currently is experimental. it has its issues, and based on #315 is going to be deprecated.

[Stophface]

@cvvergara and again: Thank you :)
Thanks for pointing the pgr_pointToEdgeNode() problem out. The authors of this book http://locatepress.com/pgrouting recommended using it...

[cvvergara]

The decision of deprecating it is recent and is not done yet.
just be careful. of when it is deprecated.

[cvvergara]

pgr_pointsAsPolygon has has been depracated on version 3.0.0
and pgr_alphaShape has been rewritten on v3.0.0
Please consider that this function will eventually be removed from pgRouting and moved to PostGIS.