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I am using OSM and facing an issue with finding the nearest road-segments to a given lat/lon point.

I have a code that uses Java Spatial Index JSI which traverses the RTree index while computing the distance between the lat/lon point and the bounding rectangle of the objects using the distance-function.

Now I am trying to implement the same functionality using PostGIS. After some reading I ended up with the following SQL query:

SELECT osm_id FROM planet_osm_line 
WHERE way <#> ST_Transform(ST_SetSRID(ST_MakePoint(:plon, :plat), 4326), 900913) < :range

where :range is the max distance in meters.

My questions are

  1. Is the use of the <#>? my understanding is that this function would calculate the distance to the edges of the BB, although I don't know how exactly.
  2. Is the transformation to 900913 correct? Does this compute the distance between 2 geometries or geographies? I am confused with the relation between SRIDs and the use of geography in the computations of distances.
  3. Does using the <#> in the WHERE clause utilize the index of the table? I found some references stating that the function will utilize the index only when used with ORDER BY clause.

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