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@jeffcatania jeffcatania/README.md

forked from mbostock/.block
Last active Aug 29, 2015
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From Wikipedia:

Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. … Epicyclic gearing systems also incorporate the use of an outer ring gear or annulus, which meshes with the planet gears.

Use the menu in the top-left to change the frame of reference, fixing the specified gear in-place.

<!DOCTYPE html>
<meta charset="utf-8">
<style>
body {
font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
width: 960px;
height: 500px;
position: relative;
}
form {
position: absolute;
top: 1em;
left: 1em;
}
path {
fill-rule: evenodd;
stroke: #333;
stroke-width: 2px;
}
.sun path {
fill: #6baed6;
}
.planet path {
fill: #9ecae1;
}
.annulus path {
fill: #c6dbef;
}
</style>
<form>
<input type="radio" name="reference" id="ref-annulus">
<label for="ref-annulus">Annulus</label><br>
<input type="radio" name="reference" id="ref-planet" checked>
<label for="ref-planet">Planets</label><br>
<input type="radio" name="reference" id="ref-sun">
<label for="ref-sun">Sun</label>
</form>
<script src="http://d3js.org/d3.v3.min.js"></script>
<script>
var width = 960,
height = 500,
radius = 80,
x = Math.sin(2 * Math.PI / 3),
y = Math.cos(2 * Math.PI / 3);
var offset = 0,
speed = 4,
start = Date.now();
var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height)
.append("g")
.attr("transform", "translate(" + width / 2 + "," + height / 2 + ")scale(.55)")
.append("g");
var frame = svg.append("g")
.datum({radius: Infinity});
frame.append("g")
.attr("class", "annulus")
.datum({teeth: 80, radius: -radius * 5, annulus: true})
.append("path")
.attr("d", gear);
frame.append("g")
.attr("class", "sun")
.datum({teeth: 16, radius: radius})
.append("path")
.attr("d", gear);
frame.append("g")
.attr("class", "planet")
.attr("transform", "translate(0,-" + radius * 3 + ")")
.datum({teeth: 32, radius: -radius * 2})
.append("path")
.attr("d", gear);
frame.append("g")
.attr("class", "planet")
.attr("transform", "translate(" + -radius * 3 * x + "," + -radius * 3 * y + ")")
.datum({teeth: 32, radius: -radius * 2})
.append("path")
.attr("d", gear);
frame.append("g")
.attr("class", "planet")
.attr("transform", "translate(" + radius * 3 * x + "," + -radius * 3 * y + ")")
.datum({teeth: 32, radius: -radius * 2})
.append("path")
.attr("d", gear);
d3.selectAll("input[name=reference]")
.data([radius * 5, Infinity, -radius])
.on("change", function(radius1) {
var radius0 = frame.datum().radius, angle = (Date.now() - start) * speed;
frame.datum({radius: radius1});
svg.attr("transform", "rotate(" + (offset += angle / radius0 - angle / radius1) + ")");
});
d3.selectAll("input[name=speed]")
.on("change", function() { speed = +this.value; });
function gear(d) {
var n = d.teeth,
r2 = Math.abs(d.radius),
r0 = r2 - 8,
r1 = r2 + 8,
r3 = d.annulus ? (r3 = r0, r0 = r1, r1 = r3, r2 + 20) : 20,
da = Math.PI / n,
a0 = -Math.PI / 2 + (d.annulus ? Math.PI / n : 0),
i = -1,
path = ["M", r0 * Math.cos(a0), ",", r0 * Math.sin(a0)];
while (++i < n) path.push(
"A", r0, ",", r0, " 0 0,1 ", r0 * Math.cos(a0 += da), ",", r0 * Math.sin(a0),
"L", r2 * Math.cos(a0), ",", r2 * Math.sin(a0),
"L", r1 * Math.cos(a0 += da / 3), ",", r1 * Math.sin(a0),
"A", r1, ",", r1, " 0 0,1 ", r1 * Math.cos(a0 += da / 3), ",", r1 * Math.sin(a0),
"L", r2 * Math.cos(a0 += da / 3), ",", r2 * Math.sin(a0),
"L", r0 * Math.cos(a0), ",", r0 * Math.sin(a0));
path.push("M0,", -r3, "A", r3, ",", r3, " 0 0,0 0,", r3, "A", r3, ",", r3, " 0 0,0 0,", -r3, "Z");
return path.join("");
}
d3.timer(function() {
var angle = (Date.now() - start) * speed,
transform = function(d) { return "rotate(" + angle / d.radius + ")"; };
frame.selectAll("path").attr("transform", transform);
frame.attr("transform", transform); // frame of reference
});
</script>
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