Our function is simple, KNN magic aside. As an input to the function, we allow geometry, as shown in the following query:
CREATE OR REPLACE FUNCTION chp04.angle_to_street (geometry) RETURNS double precision AS $$
The preceding function returns a floating-point value.
We then use a WITH statement to create a temporary table, which returns the five closest lines to our point of interest. Remember, as the index uses bounding boxes, we don't really know which line is the closest, so we gather a few extra points and then filter them based on distance. This idea is implemented in the following query:
WITH index_query as (SELECT ST_Distance($1,road.geom) as dist, degrees(ST_Azimuth($1, ST_ClosestPoint(road.geom, $1))) as azimuth ...
