location links table structure

This table lists all the links to which each location would have direct access to. The basic idea is that loading all trips to/from a location only to the closest link to it would create an artificially high level of congestion in a model with a simplified network.

Two algorithms are available for the creation of this table: all links that allow autos and pedestrians and that form the “box that encircles the location”, where one is the closest of all links and the others are the closest in directions rotated 90 degrees, starting from the vector that connects the connection and the closest link. When only one or two links are found, polaris-studio tries the intermediary angles every 45 degrees in search for links that had not been found The second algorithm simply connects the location to the closest link that allows autos.

Table Structure

Field	Type	NULL allowed	Default Value	Foreign key	Description
location	INTEGER	NO		location(location)	Foreign key reference to the location this entry refers to
link	INTEGER	NO		link(link)	Foreign key reference to the link this entry refers to
distance	REAL	YES			Straight line distance from the location to the link

(* - Primary key)

The SQL statement for table and index creation is below.

create TABLE IF NOT EXISTS "Location_Links" (
    "location"    INTEGER NOT NULL,
    "link"        INTEGER NOT NULL,
    "distance"    REAL,

    CONSTRAINT "location_fk" FOREIGN KEY("location") REFERENCES "location"("location") DEFERRABLE INITIALLY DEFERRED,
    CONSTRAINT "link_fk" FOREIGN KEY("link") REFERENCES "link"("link") DEFERRABLE INITIALLY DEFERRED
);


create INDEX IF NOT EXISTS "Location_Links_location" ON "Location_Links" ("location");
create INDEX IF NOT EXISTS "Location_Links-link" ON "Location_Links" ("link");
CREATE UNIQUE INDEX IF NOT EXISTS "Location_Links_unique" ON "Location_Links" (location, link);