Вот пример UDF.
create or replace function inside(point array, vs array)
returns string
language javascript
as $$
var point = POINT;
var vs = VS;
var x = point[0], y = point[1];
var inside = false;
for (var i = 0, j = vs.length - 1; i < vs.length; j = i++) {
var xi = vs[i][0], yi = vs[i][1];
var xj = vs[j][0], yj = vs[j][1];
var intersect = ((yi > y) != (yj > y))
&& (x < (xj - xi) * (y - yi) / (yj - yi) + xi);
if (intersect) inside = !inside;
}
return inside;
$$;
select inside(parse_json('[ 4.9, 1.2 ]')::array, parse_json('[ [ 1, 1 ], [ 1, 2 ], [ 2, 2 ], [ 2, 1 ] ]')::array);