Leaflet: flyToBounds location of bounding box returned by PostGIS

Question

I want to simply center my map on the search result of a polygon using leaflet. I thought to return the bounding box, as this is closer to what I actually need.

I want to use flyTo()

I see a possible way to do this by using Leaflet?

I have a thought to do this

SELECT ST_AsGeoJSON (geom) AS geom, Box2D(geom) as bounds, ST_YMax(Box2D(geom)) as ymax, ST_YMin(Box2D(geom)) as ymin, ST_XMax(Box2D(geom)) as xmax, ST_XMin(Box2D(geom)) as xmin FROM nation_shapes WHERE (condition)

and then pass it to

mymap.flyToBounds([[ymax, xmax],[ymin, xmin]])

Though this seems inefficient. I would like to be able to get this information from the object I am already passing back if possible, or convert something like Box2D(geom) as bounds which would be more efficient than calling it 4 times, I think.

Answer 1

I would go with...

SELECT Box2D(geom) as bounds, 
    ST_YMax(bounds) as ymax,
    ST_YMin(bounds) as ymin,
    ST_XMax(bounds) as xmax,
    ST_XMin(bounds) as xmin
    FROM nation_shapes WHERE (condition)

...as PostgreSQL's SQL engine and query planner is smart enough to figure things out and not duplicate work.

If you want to not return the bbox from the query, then

SELECT ymax, ymin, xmax, xmin FROM (
  SELECT Box2D(geom) as bounds, 
    ST_YMax(bounds) as ymax,
    ST_YMin(bounds) as ymin,
    ST_XMax(bounds) as xmax,
    ST_XMin(bounds) as xmin
    FROM nation_shapes WHERE (condition)
  )

which would be more efficient than calling it 4 times, I think.

Beware of premature optimization. Do not assume efficiency in SQL queries unless you take some time to EXPLAIN the query.