pg_routing error when generating alpha shapes

Question

When running pg_routing to generate catchment areas I got this error when running the 2 queries below:

 SQL Error [XX000]: ERROR: parse error - invalid geometry
  Hint: "se" <-- parse error at position 2 within geometry
  Position: 26

select pgr_alphaShape(
 'select
 v.id::int4, st_x(v.the_geom) as x, st_y(v.the_geom) as y
 from(
 select * from pgr_drivingDistance(''select gid as id, source,
target, cost_time as cost from roadslink_fixed'', 120829, 300)
 ) as dd
 left outer join public.roadslink_fixed_vertices_pgr v on dd.node = v.id'
);

select pgr_pointsAsPolygon(
'select
 v.id::int4, st_x(v.the_geom) as x, st_y(v.the_geom) as y
 from(
 select * from pgr_drivingDistance(''select gid as id, source,
target, cost_time as cost from roadslink_fixed'', 120829, 300)
 ) as dd
 left outer join public.roadslink_fixed_vertices_pgr v on dd.node = v.id'
);

I'm not sure why I'm getting this error, I have follow different steps to build the roads in different workshops and in all I'm getting this error. Someone has have the same issue for building catchment areas?

Answer 1

Note that pgr_pointsAsPolygon has been moved to legacy as of pgRouting 3.0.0 - I won't address this function.

---

Read the docs carefully; the full function signature

pgr_alphaShape(geometry, [spoon_radius]) RETURNS geometry

requires a GEOMETRY type as it's main parameter, while you are passing in a string literal of a SQL query.

---

Assuming the query you are trying to pass in, you'd want to run something along the lines of this:

SELECT
  pgr_alphaShape(
    -- the bracketed sub-query must return a single GEOMETRY value to get accepted as parameter to pgr_alphaShape
    (
      SELECT
        ST_Collect(v.the_geom)
      FROM
        pgr_drivingDistance(
          'SELECT gid as id, source, target, cost_time AS cost FROM roadslink_fixed',
          120829,
          300
        ) AS dd
        LEFT OUTER JOIN
        public.roadslink_fixed_vertices_pgr v
          ON dd.node = v.id
    ),
    <spoon_radius>
  )
;

---

If you need to use special/reserved characters (e.g. " or ') inside a string in locations where you need to pass in a string literal itself (expressions, function parameters, variable assignments in function bodies etc.), you can wrap string literals in $$, e.g.

• SELECT $$ ' " / $$ AS string_literal;

• or the named variant

  SELECT $SPECIAL_CHARS$ ' " / $SPECIAL_CHARS$ AS string_literals;

without escaping.