I need to figure out how to convert my X/Y-coordinates to longitude and latitude.

I do not need the exact conversion, just an approximate so I can plot it in a mapping API. I managed to estimate the following X/Y to Long/Lat:

(x, y) = 24050, 123783.3333 -> (long, lat) = (122.98, 24.46)

(x, y) = 24216.6667, 123933.3333 -> (long, lat) = (122.985339,

Can I somehow use these to come up with a formula to convert the other X/Y points?

I found another link that does what I want, but I cannot extract the formula: http://www.whoi.edu/marine/ndsf/cgi-bin/NDSFutility.cgi?form=0&from=XY&to=LatLon

In the above link, I specify the origin of X/Y in Lat/Long coordinates, and it was able to convert X/Y to Lat/Lang.

  • Why can't you get the formula? It is clearly defined in the Javascript code: whoi.edu/marine/ndsf/utility/NDSFutility.js starting in line 289.
    – Spacedman
    Commented Dec 19, 2016 at 8:08
  • Sorry that was not clear, I was able to access the javascript file but I cannot pinpoint the formula that I should follow. Commented Dec 19, 2016 at 8:28
  • Its the translate_coordinates function, which does a bunch of stuff with sines and cosines depending on the values in the formula boxes. Do you understand javascript? What language would you want to convert this to for your purposes? Also, note its not a perfect algorithm, and the web site can give nonsense lat-long for large offsets.
    – Spacedman
    Commented Dec 19, 2016 at 10:33
  • would you please confirm that the excel sheet uwgb.edu/dutchs/UsefulData/HowUseExcel.HTM is still available. Would y
    – WokiriJ
    Commented Mar 19, 2018 at 13:24
  • that page is dead, but I've linked another source Commented Sep 12, 2018 at 6:29

2 Answers 2


It is complex, due to curvature of the earth effects and where on Earth you are.

I would recommend reading this page:


If you can replicate what the spreadsheet is doing in your API, you'll have your answer.

Exactly how you do that depends on the language you're using, and I presume you've got the programming skill to do that part.

  • Thanks for this. But I think the x,y coordinates that I provided is in Mercator Projection. I found another link that does what I want, but I cannot extract the formula: whoi.edu/marine/ndsf/cgi-bin/… In the above link, I specify the origin of xy in lat-long coordinates, and it was able to convert xy to lat-lang Commented Dec 19, 2016 at 6:47
  • The link I gave is for UTM projection, which stands for Universal Transverse Mercator, i.e. its what you want. But you'll need to know which zone you are in for the spreadsheet to give answers. You can use Google Earth, and set the coordinate system to UTM. It will say in the bottom right zone plus coordinates of the current view. Go to your area and find your zone, then the UTM conversion spreadsheet will become useful. Commented Dec 19, 2016 at 7:02

//Sample "convert xy to latlong" by pod ArcGis:

for item in (GeometryDataXYValue)!{
        let xValue = item.paths?.ofX
        let yValue = item.paths?.ofY

        //recieve x y point
        currentPoint = AGSPoint(x: xValue!, y: yValue!, spatialReference: AGSSpatialReference.webMercator()) 

        //convert to lat long by AGSSpatialReference.wgs84()

       if  let aReference = AGSGeometryEngine.projectGeometry(currentPoint!, to: AGSSpatialReference.wgs84()) as? AGSPoint {
            currentPoint = aReference
    var long:Double = currentPoint!.x
    var lat: Double = currentPoint!.y
    print("value long lat =  \(long , lat)")
  • not sure what pod ArcGIS means, can you clarify in your answer.
    – nmtoken
    Commented Jul 20, 2018 at 8:33
  • I use pod of ArcGIS to import some process method in map to bring use in my code use method for convert data point xy to lat long. if you use another map I think you can't use this method
    – Papon Smc
    Commented Jul 23, 2018 at 6:46
  • this is pod developers.arcgis.com/ios
    – Papon Smc
    Commented Jul 23, 2018 at 6:47

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