D3 Examples - Link nodes to avoid node/link overlap

Link nodes to avoid node/link overlap

This gist demonstrates the inserting of link nodes to avoid node/link overlap.

This simple force-directed graph shows character co-occurence in *Les Misérables*. A physical simulation of charged particles and springs places related characters in closer proximity, while unrelated characters are farther apart. Layout algorithm inspired by [Tim Dwyer](http://www.csse.monash.edu.au/~tdwyer/) and [Thomas Jakobsen](http://web.archive.org/web/20080410171619/http://www.teknikus.dk/tj/gdc2001.htm). Data based on character coappearence in Victor Hugo's *Les Misérables*, compiled by [Donald Knuth](http://www-cs-faculty.stanford.edu/~uno/sgb.html).

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<!DOCTYPE html>
<meta charset="utf-8">
<style>
​
.node {
  stroke: #fff;
  stroke-width: 1.5px;
}
​
.link {
  stroke: #999;
  stroke-opacity: .6;
}
​
</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>
​
var width = 960,
    height = 500;
​
var color = d3.scale.category20();
​
var force = d3.layout.force()
    .charge(-120)
    .linkDistance(30)
    .size([width, height]);
​
var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);
​
d3.json("miserables.json", function(error, graph) {
​
  var linkNodes = [];
​
  graph.links.forEach(function(link) {
    linkNodes.push({
      source: graph.nodes[link.source],
      target: graph.nodes[link.target]
    });
  });
​
  force
      .nodes(graph.nodes.concat(linkNodes))
      .links(graph.links)
      .start();
​
  var link = svg.selectAll(".link")
      .data(graph.links)
    .enter().append("line")
      .attr("class", "link")
      .style("stroke-width", function(d) { return Math.sqrt(d.value); });
​
  var node = svg.selectAll(".node")
      .data(graph.nodes)
    .enter().append("circle")
      .attr("class", "node")
      .attr("r", 5)
      .style("fill", function(d) { return color(d.group); })
      .call(force.drag);
​
  node.append("title")
      .text(function(d) { return d.name; });
​
  var linkNode = svg.selectAll(".link-node")
      .data(linkNodes)
    .enter().append("circle")
      .attr("class", "link-node")
      .attr("r", 2)
      .style("fill", "#ccc");
​
  force.on("tick", function() {
    link.attr("x1", function(d) { return d.source.x; })
        .attr("y1", function(d) { return d.source.y; })
        .attr("x2", function(d) { return d.target.x; })
        .attr("y2", function(d) { return d.target.y; });
​
    node.attr("cx", function(d) { return d.x; })
        .attr("cy", function(d) { return d.y; });
​
    //linkNode.attr("cx", function(d) { return d.x = (d.source.x + d.target.x) * 0.5; })
    //    .attr("cy", function(d) { return d.y = (d.source.y + d.target.y) * 0.5; });
  });
});
​
</script>
​
    