[pgrouting-dev] K-Shortest Path round-trip pattern question

pgRouting pgrouting-dev
1

Hi list,

I am facing an issue about K-Shortest Path round-trip pattern.

When I specified same source and target ids, then pgr_ksp results are
invalid like this.

sampledata=# SELECT seq, id1 AS route, id2 AS node, id3 AS edge, cost
FROM pgr_ksp(
   'SELECT id, source, target, cost FROM edge_table',
   1, 1, 4, false
);
seq | route | node | edge | cost
-----+-------+------+-------------+-----------------------
   0 | 0 | 1 | -2147483648 | 1.79769313486232e+308
   1 | 0 | 1 | -1 | 0
(2 rows)

I think that the results should be as follows,
because in my understanding, K-Shortest Path should support round-trip pattern.

seq | route | node | edge | cost
-----+-------+------+-------------+-----------------------
   0 | 0 | 1 | 1 | 1
   1 | 0 | 2 | 1 | 1
   2 | 0 | 1 | -1 | 0
   3 | 1 | 1 | 1 | 1
   : | : | : | : | :

But is my understanding wrong ?
(Shouldn't K-Shortest Path support round-trip case ?)

If my understanding is wrong, does someone know
how to support round-trip case ?

About above pgr_ksp issue, I created the ticket to here.
[pgr_ksp returns invalid one route when source and target are same #287]

Regards,

--
Ko Nagase (長瀬 興)
Georepublic Japan
mail: nagase@georepublic.co.jp
web: http://georepublic.co.jp

2

Nagase-san,

I answered this in the user list.

Basically there is not roundtrip support for any shortest path algorithm. Shorthest path is point to point and the shortest path from a point to itself is defined as zero.

-Steve

On 2/7/2015 3:23 AM, Ko Nagase wrote:

Hi list,

I am facing an issue about K-Shortest Path round-trip pattern.

When I specified same source and target ids, then pgr_ksp results are
invalid like this.

sampledata=# SELECT seq, id1 AS route, id2 AS node, id3 AS edge, cost
  FROM pgr_ksp(
    'SELECT id, source, target, cost FROM edge_table',
    1, 1, 4, false
  );
  seq | route | node | edge | cost
-----+-------+------+-------------+-----------------------
    0 | 0 | 1 | -2147483648 | 1.79769313486232e+308
    1 | 0 | 1 | -1 | 0
(2 rows)

I think that the results should be as follows,
because in my understanding, K-Shortest Path should support round-trip pattern.

  seq | route | node | edge | cost
-----+-------+------+-------------+-----------------------
    0 | 0 | 1 | 1 | 1
    1 | 0 | 2 | 1 | 1
    2 | 0 | 1 | -1 | 0
    3 | 1 | 1 | 1 | 1
    : | : | : | : | :

But is my understanding wrong ?
(Shouldn't K-Shortest Path support round-trip case ?)

If my understanding is wrong, does someone know
how to support round-trip case ?

About above pgr_ksp issue, I created the ticket to here.
[pgr_ksp returns invalid one route when source and target are same #287]
https://github.com/pgRouting/pgrouting/issues/287

Regards,

3

Hi Stephen,

Thanks for your answer.

2015-02-08 0:09 GMT+09:00 Stephen Woodbridge <woodbri@swoodbridge.com>:

Basically there is not roundtrip support for any shortest path algorithm.
Shorthest path is point to point and the shortest path from a point to
itself is defined as zero.

Okay.
Thanks for clarification.

Regards,

On 2/7/2015 3:23 AM, Ko Nagase wrote:

Hi list,

I am facing an issue about K-Shortest Path round-trip pattern.

When I specified same source and target ids, then pgr_ksp results are
invalid like this.

sampledata=# SELECT seq, id1 AS route, id2 AS node, id3 AS edge, cost
  FROM pgr_ksp(
    'SELECT id, source, target, cost FROM edge_table',
    1, 1, 4, false
  );
  seq | route | node | edge | cost
-----+-------+------+-------------+-----------------------
    0 | 0 | 1 | -2147483648 | 1.79769313486232e+308
    1 | 0 | 1 | -1 | 0
(2 rows)

I think that the results should be as follows,
because in my understanding, K-Shortest Path should support round-trip
pattern.

  seq | route | node | edge | cost
-----+-------+------+-------------+-----------------------
    0 | 0 | 1 | 1 | 1
    1 | 0 | 2 | 1 | 1
    2 | 0 | 1 | -1 | 0
    3 | 1 | 1 | 1 | 1
    : | : | : | : | :

But is my understanding wrong ?
(Shouldn't K-Shortest Path support round-trip case ?)

If my understanding is wrong, does someone know
how to support round-trip case ?

About above pgr_ksp issue, I created the ticket to here.
[pgr_ksp returns invalid one route when source and target are same #287]
pgr_ksp returns invalid one route when source and target are same · Issue #287 · pgRouting/pgrouting · GitHub

Regards,

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--
Ko Nagase (長瀬 興)
Georepublic Japan
mail: nagase@georepublic.co.jp
web: http://georepublic.co.jp