Orthographic Pulse

Experimenting with d3.geoCircle to create animated circles on an orthographic projection.

This animation needs to be tweened because d3.transition doesn't really work with geoCircle.

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <script src="https://d3js.org/topojson.v2.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
    
    .ocean {
      fill: #dadada;
    }
    
    .geoCircle {
      fill: red;
      fill-opacity: 0.5;
      stroke: red;
      stroke-width: 2px;
    }
  </style>
</head>

<body>
  <script>
    const margin = {top: 50, right: 0, bottom: 50, left: 0};
    
    const width = 960 - margin.left - margin.right,
    		height = 500 - margin.top - margin.bottom;
    
    var svg = d3.select("body").append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
    	.append("g")
    		.attr("transform", "translate(" + margin.left + "," + margin.top + ")");
    
    const config = {
      radius: 90 * 0.5,
      center: [0.1278, 51.5074]
		}
		
    d3.json("https://unpkg.com/world-atlas@1.1.4/world/110m.json", (error, world) => {
      var land = topojson.feature(world, world.objects.land);
      
      var projection = d3.geoOrthographic()
      	.fitSize([width, height], land)
      	.clipAngle(90)
        .precision(0);
      
      var path = d3.geoPath()
        .projection(projection);
      
      var geoCircle = d3.geoCircle();
      
     	var ocean = svg.append("circle")
      	.attr("class", "ocean")
      	.attr("cx", width / 2)
      	.attr("cy", height / 2)
        .attr("r", height / 2);
      
      var earth = svg.append("path")
      	.datum(land)
      	.attr("d", path);
      
      var circle = svg.append("path")
      	.datum({endAngle: 0})
      	.attr("class", "geoCircle")
      	.attr("d", d => path(geoCircle.center(config.center).radius(d.endAngle)()));
      
      circle.transition()
      	.delay(1000)
      	.duration(4000)
      	.ease(d3.easeLinear)
      	.attrTween("d", geoCircleTween(config.radius));
      
      function geoCircleTween(newAngle) {
        return function(d) {
          var interpolate = d3.interpolate(d.endAngle, newAngle);
          return function(t) {
            d.endAngle = interpolate(t);
            return path(geoCircle.center(config.center).radius(d.endAngle)());
          };
        };
      }      
      
    });

</script>
</body>

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

https://d3js.org/topojson.v2.min.js