Increase the BBOX size but keep the ratio (Lon/Lat)

Question

I have a Bbox that is defined by the following values:

xmin: 11.555333537980914 
ymin: 47.76067947037518 
xmax: 11.995692579075694 
ymax: 48.281587762758136

I would like to increase the size of this Bbox but keep the ratio. One approach I tried is to calculate the middle point of the Bbox and calculate a new Bbox with the value of radius increased by 50%. The problem: the ratio gets lost.

How could I increase the size of Bbox to 50% but keep the ratio.

Answer 1

Perhaps ST_Expand is what you're looking for. You could first calculate the area of the input bbox using ST_Area and then use the output as a unit to expand the bbox.

SELECT            -- here you can play with different sizes
  ST_Expand(geom, ST_Area(geom)/2) 
FROM yourtable;

Example:

WITH j (geom) AS (
  SELECT ST_MakeEnvelope(11.555333537980914,
                         47.76067947037518,
                         11.995692579075694,
                         48.281587762758136,4326)
)
SELECT 
  ST_Expand(geom,ST_Area(geom)/2) 
FROM j;

The image below represents the result set. The inner bbox is the one you provided and the outer one was created with ST_Expand.

Demo: db<>fiddle