SouthWest and NorthEast Points

Question

I am developing an iphone application which uses google API's.I have a set of latitudes and logitudes .I need to find the South west and North East points from these points .How can i do this?

thanks in advance

Answer 1

Given: A point (LAT, LNG) A distance or radius DIST 1° of latitude ~= 69 miles ~= 111 kms 1° of longitude ~= cos(latitude)*69 ~= cos(latitude)*111

The SW point is: lng_sw = LNG - (DIST / (abs(cos(radians(LAT))) * 111)) lat_sw = LAT - (DIST / 111)

The NE point is: lng_ne = LNG + (DIST / (abs(cos(radians(LAT))) * 111)) lat_ne = LAT + (DIST / 111)

If you use miles as your unit of measure use 69 instead of 111.

Answer 2

This is C# code if anybody needs

 private double DegreeToRadian(double angle) {
     return Math.PI * angle / 180.0;
 }

 private bool CalculateNeSw(double distance, double lat, double lng, out MapPoint[] points) {
        /*
         * 1° of latitude ~= 69 miles ~= 111 kms, 1° of longitude ~= cos(latitude)*69 ~= cos(latitude)*111
         * SW.LNG = LNG - (DIST / abs(cos(radians(LAT))) * 111), SW.LAT = LAT - (DIST / 111)
         * NE.LNG = LNG + (DIST / abs(cos(radians(LAT))) * 111), NE.LAT = LAT + (DIST / 111)
         */
        points = new MapPoint[2];
        try {
            double deltaLat = distance / 69;
            double deltaLng = distance / Math.Abs(Math.Cos(DegreeToRadian(lat)) * 69);

            /* South-West */
            points[1] = new MapPoint {
                Lng = (lng - deltaLng).ToString(),
                Lat = (lat - deltaLat).ToString(),
                IsSet = true,
                FormattedAddress = "South-West"
            };

            /* North-East */
            points[0] = new MapPoint {
                Lng = (lng + deltaLng).ToString(),
                Lat = (lat + deltaLat).ToString(),
                IsSet = true,
                FormattedAddress = "North-East"
            };

            return true;
        }
        catch (Exception ex) {
            return false;
        }}

Notes:

• MapPoint is a simple Data class with Lat/Lon properties

• I used miles ==> 69