ggirou/center.dart

## center.dart
import 'dart:convert';
import 'dart:html';
import 'dart:math';
import 'dart:svg' as svg;

main() {
  HttpRequest.getString('svg-datas.json').then(JSON.decode).then(calculateGravity);
}

calculateGravity(Map<String, Map> paths) {
  paths.forEach((country, data) {
    var path = data['path'];
    var el = new svg.PathElement()..setAttribute('d', path);
    List<Point> points = el.pathSegList
        .where((ps) => !(ps is svg.PathSegClosePath))
        .map((p) => new Point(p.x, p.y)).toList();
    var g = gravity(points);

    print("""  "$country": {
    "path": "$path",
    "center": {
      "x": ${g.x},
      "y": ${g.y}
    }
  },""");
  });
}

Point gravity(List<Point> points) {
  num sumArea = 0, sumX = 0, sumY = 0;
  for (int i = 0; i < points.length; i++) {
    var i_p = (i + 1) % points.length;
    var g = points[i].x * points[i_p].y - points[i_p].x * points[i].y;
    sumArea += g;
    sumX += (points[i].x + points[i_p].x) * g;
    sumY += (points[i].y + points[i_p].y) * g;
  }
  sumArea = 3 * sumArea;
  return new Point((sumX / sumArea).round(), (sumY / sumArea).round());
}

## center.html
<!DOCTYPE html>

<html>
  <head>
  	<meta charset="utf-8">
  	<meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>center</title>
  </head>

  <body>
    <p id="text"></p>
    <script type="application/dart" src="center.dart"></script>
    <!-- for this next line to work, your pubspec.yaml file must have a dependency on 'browser' -->
    <script src="packages/browser/dart.js"></script>
  </body>
</html>
	import 'dart:convert';
	import 'dart:html';
	import 'dart:math';
	import 'dart:svg' as svg;

	main() {
	HttpRequest.getString('svg-datas.json').then(JSON.decode).then(calculateGravity);
	}

	calculateGravity(Map<String, Map> paths) {
	paths.forEach((country, data) {
	var path = data['path'];
	var el = new svg.PathElement()..setAttribute('d', path);
	List<Point> points = el.pathSegList
	.where((ps) => !(ps is svg.PathSegClosePath))
	.map((p) => new Point(p.x, p.y)).toList();
	var g = gravity(points);

	print(""" "$country": {
	"path": "$path",
	"center": {
	"x": ${g.x},
	"y": ${g.y}
	}
	},""");
	});
	}

	Point gravity(List<Point> points) {
	num sumArea = 0, sumX = 0, sumY = 0;
	for (int i = 0; i < points.length; i++) {
	var i_p = (i + 1) % points.length;
	var g = points[i].x * points[i_p].y - points[i_p].x * points[i].y;
	sumArea += g;
	sumX += (points[i].x + points[i_p].x) * g;
	sumY += (points[i].y + points[i_p].y) * g;
	}
	sumArea = 3 * sumArea;
	return new Point((sumX / sumArea).round(), (sumY / sumArea).round());
	}
	<!DOCTYPE html>

	<html>
	<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>center</title>
	</head>

	<body>
	<p id="text"></p>
	<script type="application/dart" src="center.dart"></script>
	<!-- for this next line to work, your pubspec.yaml file must have a dependency on 'browser' -->
	<script src="packages/browser/dart.js"></script>
	</body>
	</html>