transit walk table structure

This table is the junction of two different types of links: * Network links (from the links table) that can be traversed by walk * Access links connecting stops and micro-mobility docks to the network

This network is static and should be re-created any time there are changes in the transit data (e.g. import of a new GTFS feed), or whenever new micromobility docks are added to the supply database.

It important to understand that the number of links in this network is substantially larger than in the links table because it has links connecting each stop/dock to the physical network, as well as links connecting transit stops (and docks) stops directly to each other whenever they are very close (the distance between them is half of that between them and the physical network.

Physical links are also broken to allow stops to be connected by walk in the middle of links, where stops are actually located. We attempt to reduce the number of link breaks by combining access links into the same point whenever possible and without penalizing agents with substantially longer walk distances.

Table Structure

Field	Type	NULL allowed	Default Value	Foreign key	Description
walk_link*	INTEGER	NO			Walk link ID
from_node	INTEGER	NO			node start for the link. Can be a regular network node or as virtual node created to articulate the network
to_node	INTEGER	NO			same as the from_node but for the end of the link
bearing_a	INTEGER	NO	0		Geographic bearing at the start of the link
bearing_b	INTEGER	NO	0		Geographic bearing at the end of the link
length	REAL	NO			Length of the link in meters
ref_link	INTEGER	NO	0		Reference to the link in the roadway network (link table), if any
geo	LINESTRING	NO	‘’

(* - Primary key)

The SQL statement for table and index creation is below.

CREATE TABLE IF NOT EXISTS "Transit_Walk" (
    walk_link INTEGER  NOT NULL PRIMARY KEY AUTOINCREMENT,
    from_node INTEGER       NOT NULL,
    to_node   INTEGER       NOT NULL,
    bearing_a INTEGER  NOT NULL DEFAULT 0,
    bearing_b INTEGER  NOT NULL DEFAULT 0,
    length    REAL     NOT NULL,
    ref_link  INTEGER  NOT NULL default 0
);

SELECT AddGeometryColumn('Transit_Walk', 'geo', SRID_PARAMETER, 'LINESTRING', 'XY', 1);

UPDATE SQLITE_SEQUENCE SET seq = 3000000 WHERE name = 'Transit_Walk';

SELECT CreateSpatialIndex('Transit_Walk' , 'geo');


CREATE INDEX IF NOT EXISTS transit_walk_from_node ON Transit_Walk (from_node);

CREATE INDEX IF NOT EXISTS transit_walk_to_node ON Transit_Walk (to_node);