Elliptic / scaled Polylabel with D3

Testing @mourner's polylabel with D3.

Orange dot = centroid ; white dot = normal polylabel; green dot = elliptic polylabel.

In this variant from Polylabel with D3 we set different scales for x and y, so as to find the "largest ellipse" to accomodate "horizontal" text labels (the ellipse ratio would match the text bbox ratio).

Built with blockbuilder.org, base map by @mbostock.

<!DOCTYPE html>
<meta charset="utf-8">
<style>

.stroke {
  fill: none;
  stroke: #000;
  stroke-width: 3px;
}

.fill {
  fill: #fff;
}

.graticule {
  fill: none;
  stroke: #777;
  stroke-width: 0.5px;
  stroke-opacity: 0.5;
}

.land {
  fill: #ccc;
}

.boundary {
  fill: none;
  stroke: #555;
  stroke-width: 0.5px;
}

</style>
<svg width="960" height="484"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://d3js.org/d3-geo-projection.v2.min.js"></script>
<script src="https://d3js.org/topojson.v1.min.js"></script>
<script src="polylabel.js"></script>
<script>

var svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height");

var projection = d3.geoRobinson()
.rotate([-10.5,0])
    .translate([width / 2, height / 2])
    .precision(0.1);

var graticule = d3.geoGraticule();

var path = d3.geoPath()
    .projection(projection);

var defs = svg.append("defs");

defs.append("path")
    .datum({type: "Sphere"})
    .attr("id", "sphere")
    .attr("d", path);

defs.append("clipPath")
    .attr("id", "clip")
  .append("use")
    .attr("xlink:href", "#sphere");

svg.append("use")
    .attr("class", "stroke")
    .attr("xlink:href", "#sphere");

svg.append("use")
    .attr("class", "fill")
    .attr("xlink:href", "#sphere");

svg.append("path")
    .datum(graticule)
    .attr("class", "graticule")
    .attr("clip-path", "url(#clip)")
    .attr("d", path);

var lines = svg.append("g"),
      circles = svg.append("g");
  
  console.clear()
  
d3.json("https://unpkg.com/visionscarto-world-atlas@0.0.6/world/110m.json", function(error, world) {
  if (error) throw error;

if (true)
  svg.insert("path", ".graticule")
      .datum(topojson.feature(world, world.objects.countries))
      .attr("class", "land")
      .attr("clip-path", "url(#clip)")
      .attr("d", path);

if (true)
  svg.insert("path", ".graticule")
      .datum(topojson.mesh(world, world.objects.countries, function(a, b) { return a !== b; }))
      .attr("class", "boundary")
      .attr("clip-path", "url(#clip)")
      .attr("d", path);
  
  var w = topojson.feature(world, world.objects.countries);
  w.features.forEach(function(d, i){

// get the larget sub-polygon's coordinates
    var coord = d.geometry.coordinates;
    if (d.geometry.type == 'MultiPolygon') {
      var u = d3.scan(
        coord.map(function(p){
          return -d3.polygonArea(p[0]);
        })
      );
      coord = coord[u];
    }

var o = projection(d3.geoCentroid(d));
     var n = polylabel([coord[0].map(projection)]);

// Find the best *ellipse* with x/y ratio = alpha
    var alpha = 4;
    var m = polylabel([coord[0].map(projection).map(function(d){
          d[0] /= alpha;
          return d;
        })]);
    m[0] *= alpha;

lines.append('line')
      .attr('x1', o[0])
      .attr('y1', o[1])
      .attr('x2', n[0])
      .attr('y2', n[1])
      .attr('stroke', 'green')
      .attr('stroke-width', 1);
    lines.append('line')
      .attr('x1', o[0])
      .attr('y1', o[1])
      .attr('x2', m[0])
      .attr('y2', m[1])
      .attr('stroke', 'green')
      .attr('stroke-width', 1);
    circles.append('circle')
      .attr('cx', o[0])
      .attr('cy', o[1])
      .attr('r', 2)
      .attr('stroke', 'orange')
      .attr('fill', 'yellow')
      .attr('stroke-width', 1);
    circles.append('circle')
      .attr('cx', n[0])
      .attr('cy', n[1])
      .attr('r', 2)
      .attr('stroke', 'green')
      .attr('fill', 'white')
      .attr('stroke-width', 1);
    circles.append('circle')
      .attr('cx', m[0])
      .attr('cy', m[1])
      .attr('r', 3)
      .attr('stroke', 'green')
      .attr('fill', 'green');

});

</script>

https://d3js.org/d3.v4.min.js

https://d3js.org/d3-geo-projection.v2.min.js

https://d3js.org/topojson.v1.min.js