Calculate the center point of multiple latitude/longitude coordinate pairs
Solution 1:
Thanks! Here is a C# version of OP's solutions using degrees. It utilises the System.Device.Location.GeoCoordinate class
public static GeoCoordinate GetCentralGeoCoordinate(
IList<GeoCoordinate> geoCoordinates)
{
if (geoCoordinates.Count == 1)
{
return geoCoordinates.Single();
}
double x = 0;
double y = 0;
double z = 0;
foreach (var geoCoordinate in geoCoordinates)
{
var latitude = geoCoordinate.Latitude * Math.PI / 180;
var longitude = geoCoordinate.Longitude * Math.PI / 180;
x += Math.Cos(latitude) * Math.Cos(longitude);
y += Math.Cos(latitude) * Math.Sin(longitude);
z += Math.Sin(latitude);
}
var total = geoCoordinates.Count;
x = x / total;
y = y / total;
z = z / total;
var centralLongitude = Math.Atan2(y, x);
var centralSquareRoot = Math.Sqrt(x * x + y * y);
var centralLatitude = Math.Atan2(z, centralSquareRoot);
return new GeoCoordinate(centralLatitude * 180 / Math.PI, centralLongitude * 180 / Math.PI);
}
Solution 2:
The simple approach of just averaging them has weird edge cases with angles when they wrap from 359' back to 0'.
A much earlier question on SO asked about finding the average of a set of compass angles.
An expansion of the approach recommended there for spherical coordinates would be:
- Convert each lat/long pair into a unit-length 3D vector.
- Sum each of those vectors
- Normalise the resulting vector
- Convert back to spherical coordinates
Solution 3:
I found this post very useful so here is the solution in PHP. I've been using this successfully and just wanted to save another dev some time.
/**
* Get a center latitude,longitude from an array of like geopoints
*
* @param array data 2 dimensional array of latitudes and longitudes
* For Example:
* $data = array
* (
* 0 = > array(45.849382, 76.322333),
* 1 = > array(45.843543, 75.324143),
* 2 = > array(45.765744, 76.543223),
* 3 = > array(45.784234, 74.542335)
* );
*/
function GetCenterFromDegrees($data)
{
if (!is_array($data)) return FALSE;
$num_coords = count($data);
$X = 0.0;
$Y = 0.0;
$Z = 0.0;
foreach ($data as $coord)
{
$lat = $coord[0] * pi() / 180;
$lon = $coord[1] * pi() / 180;
$a = cos($lat) * cos($lon);
$b = cos($lat) * sin($lon);
$c = sin($lat);
$X += $a;
$Y += $b;
$Z += $c;
}
$X /= $num_coords;
$Y /= $num_coords;
$Z /= $num_coords;
$lon = atan2($Y, $X);
$hyp = sqrt($X * $X + $Y * $Y);
$lat = atan2($Z, $hyp);
return array($lat * 180 / pi(), $lon * 180 / pi());
}
Solution 4:
Very useful post! I've implemented this in JavaScript, hereby my code. I've used this successfully.
function rad2degr(rad) { return rad * 180 / Math.PI; }
function degr2rad(degr) { return degr * Math.PI / 180; }
/**
* @param latLngInDeg array of arrays with latitude and longtitude
* pairs in degrees. e.g. [[latitude1, longtitude1], [latitude2
* [longtitude2] ...]
*
* @return array with the center latitude longtitude pairs in
* degrees.
*/
function getLatLngCenter(latLngInDegr) {
var LATIDX = 0;
var LNGIDX = 1;
var sumX = 0;
var sumY = 0;
var sumZ = 0;
for (var i=0; i<latLngInDegr.length; i++) {
var lat = degr2rad(latLngInDegr[i][LATIDX]);
var lng = degr2rad(latLngInDegr[i][LNGIDX]);
// sum of cartesian coordinates
sumX += Math.cos(lat) * Math.cos(lng);
sumY += Math.cos(lat) * Math.sin(lng);
sumZ += Math.sin(lat);
}
var avgX = sumX / latLngInDegr.length;
var avgY = sumY / latLngInDegr.length;
var avgZ = sumZ / latLngInDegr.length;
// convert average x, y, z coordinate to latitude and longtitude
var lng = Math.atan2(avgY, avgX);
var hyp = Math.sqrt(avgX * avgX + avgY * avgY);
var lat = Math.atan2(avgZ, hyp);
return ([rad2degr(lat), rad2degr(lng)]);
}
Solution 5:
Javascript version of the original function
/**
* Get a center latitude,longitude from an array of like geopoints
*
* @param array data 2 dimensional array of latitudes and longitudes
* For Example:
* $data = array
* (
* 0 = > array(45.849382, 76.322333),
* 1 = > array(45.843543, 75.324143),
* 2 = > array(45.765744, 76.543223),
* 3 = > array(45.784234, 74.542335)
* );
*/
function GetCenterFromDegrees(data)
{
if (!(data.length > 0)){
return false;
}
var num_coords = data.length;
var X = 0.0;
var Y = 0.0;
var Z = 0.0;
for(i = 0; i < data.length; i++){
var lat = data[i][0] * Math.PI / 180;
var lon = data[i][1] * Math.PI / 180;
var a = Math.cos(lat) * Math.cos(lon);
var b = Math.cos(lat) * Math.sin(lon);
var c = Math.sin(lat);
X += a;
Y += b;
Z += c;
}
X /= num_coords;
Y /= num_coords;
Z /= num_coords;
var lon = Math.atan2(Y, X);
var hyp = Math.sqrt(X * X + Y * Y);
var lat = Math.atan2(Z, hyp);
var newX = (lat * 180 / Math.PI);
var newY = (lon * 180 / Math.PI);
return new Array(newX, newY);
}