Planetary Rings

An attempt to use d3 to simulate planetary rings.

The same equitorial feature is drawn 10 times with projections that are increaslingly zoomed in and with a slightly enlarged clip radius.

This uses a looped append, which should normally not be used.

Based off of this rotating orthographic, upgraded to v4.

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

path {
  fill: none;
  stroke-linejoin: round;
}

.sphere,
.graticule {
  stroke: #aaa;
  fill: white;
}

.equator {
  stroke-width: 2px;
}

</style>
<body>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var width = 960,
    height = 500,
    rotate = [10, -10],
    velocity = [.003, -.001],
    time = Date.now();

var projection = d3.geoOrthographic()
    .scale(100)
    .translate([width / 2, height / 2])
	.rotate([20,-30,30])
    .clipAngle(90 + 1e-6)
    .precision(.3);
		
var colors = ["#ceb8b8","#ead6b8","#e3e0c0","#bfbdaf","#cecece"];
var dashArray = [25,1,10,1,12,1,28,1,17,1,35,1,5,1];

var path = d3.geoPath()
    .projection(projection);
	
var projections = d3.range(10).map(function(d) {
	var s = 100 * (1 + 0.25 + d/20   )
	return d3.geoOrthographic()
	  .scale(s)
      .translate([width / 2, height / 2])
	  .clipAngle(Math.pow(s/100,0.5)*90*1.25-Math.pow(d/5,2) + (1-Math.abs(0.5-d/5))*1 )
      .precision(.3)
	  .rotate([20,-30,30])
})

var graticule = d3.geoGraticule();

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);
	
var feature = {"type":"Feature","geometry":{"type":"Polygon","coordinates":[[[179,0.1],[179,-0.1],[90,-0.1],[0,-0.1],[-90,-0.1],[-179,-0.1],[-179,0.1],[-90,0.1],[0,0.1],[90,0.1],[179,0.1]]]},"properties":null }

var sphere = svg.append("path")
    .datum({type: "Sphere"})
    .attr("class", "sphere")
    .attr("d", path);

var grat = svg.append("path")
    .datum(graticule)
    .attr("class", "graticule")
    .attr("d", path);

d3.range(10).forEach(function(k) {
	var ringsPath = d3.geoPath().projection(projections[k])
	svg.append("path")
	 .datum(feature)
	 .attr("class","equator")
	 .attr("d",ringsPath)
	 .attr("stroke",colors[k%5])
	 .style("stroke-dasharray",dashArray);
})

var feature = svg.selectAll("path");

d3.timer(function() {
	var dt = Date.now() - time;
	projection.rotate([rotate[0] + velocity[0] * dt, rotate[1] + velocity[1] * dt]);
	
	// update graticule and sphere
	grat.attr("d", path);
	sphere.attr("d",path);

// update the projection for each ring
	projections.forEach(function(d,i) {
		d.rotate( [(rotate[0] + 20 * i) + velocity[0] * dt, rotate[1] + velocity[1] * dt]);
	})

// update each ring
    d3.selectAll(".equator").each(function(d,i) {
		var p = d3.select(this);
		var r = projection.rotate();
		var newPath = d3.geoPath().projection(projections[i])
		p.attr("d",newPath);		
	})
});

</script>

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