Convert x/y geo coordinates to lat/long

Example payload with geo coordinates:

{
    "GeographicalPosition": {
        "X": 6580203,
        "Y": 1629016
    },
    "Id": "e4e697cd-ef44-423e-b853-012ab8879159",
    "Name": "Bågspännaren",
    "TimeCreated": "/Date(1330524285303+0100)/",
    "TimeUpdated": "/Date(1330524370163+0100)/"
}

Links

JavaScript converter - https://github.com/proj4js/proj4js
http://spatialreference.org/
Online converter - https://www.whoi.edu/marine/ndsf/utility/NDSFutility.html

buren / stockholm-api

Convert x/y geo coordinates to lat/long #8