Orthogonal Distance between polygons in PostGIS

Question

I have a point on line with two polygons on both sides. The scenario is shown in the following:

Now, I would like to compute the perpendicular distance between two polygons (for example, yellow line) using a PostGIS query. I was wondering if someone could suggest me how to do that?

EDIT1:

Above given scenario was an example. There can be complications in scenarios having streets, points and polygons. For example, the side parallel to street may not always be there.

Scenario_2:

Scenario_3:

EDIT2

Scenario_4

I want to calculate the perpendicular distance only where there is a point on line. I understand there can be exceptions in this, as point by @JGH.

Answer 1

Assuming your data is projected and that the distance between the points and the two nearest polygon is the one you are looking for, you can compute the distance from each point to the two polygons and make the sum.

1) compute the distance. Restrict the search to a reasonable distance, maybe twice the expected largest distance. Make sure the geometries are indexed!!

SELECT pt.gid point_gid, plg.gid polygon_gid, ST_Distance(pt.geom, plg.geom) distance
    FROM pointlayer pt, polygonlayer plg 
    WHERE ST_Distance(pt.geom, plg.geom) < 50
    ORDER BY pt.gid, ST_Distance(pt.geom, plg.geom);

2) For each point, get the two closest polygons using the partition function

SELECT
  point_gid,  polygon_gid, distance
FROM (
  SELECT
    ROW_NUMBER() OVER (PARTITION BY point_gid ORDER BY distance asc) AS rank,
    t.*
  FROM
    [distanceTable] t) top_n
WHERE
  top_n.rank <= 2;

3) agregate the result and keep track of which polygons were used

select  point_gid, 
        sum(distance) streetwidth, 
        string_agg(polygon_gid || ' - ' || distance,';') polyid_dist_info
from [top_2_dist dst]
group by dst.point_gid;

All together:

SELECT
  point_gid, 
  sum(distance) streetwidth, 
  string_agg(polygon_gid || ' - ' || distance,';') polyid_dist_info
FROM (
  SELECT
    ROW_NUMBER() OVER (PARTITION BY point_gid ORDER BY distance asc) AS rank,
    t.*
   FROM
    ( SELECT pt.gid point_gid, 
             plg.gid polygon_gid, 
             ST_Distance(pt.geom, plg.geom) distance
        FROM pointlayer pt, polygonlayer plg 
        WHERE ST_Distance(pt.geom, plg.geom) < 50
     ) t
 ) top_n
WHERE
  top_n.rank <= 2
GROUP BY point_gid;