Calculating the outer tangent of two circles using this solution on Stackoverflow by Markus Jarderot.
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Outer Tangent
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license: gpl-3.0 |
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<!DOCTYPE html> | |
<meta charset="utf-8"> | |
<style> | |
.circle { | |
fill-opacity: .1; | |
fill: #000; | |
stroke-opacity: .5; | |
stroke: #000; | |
stroke-width: 2px; | |
} | |
line { | |
stroke-opacity: .8; | |
stroke: #0b3; | |
stroke-width: 2px; | |
} | |
</style> | |
<svg width="960" height="500"></svg> | |
<script src="//d3js.org/d3.v3.min.js" charset="utf-8"></script> | |
<script> | |
// Based on http://stackoverflow.com/a/12037737 | |
function outerTangent(x1, y1, r1, x2, y2, r2) { | |
var dx = x2 - x1; | |
var dy = y2 - y1; | |
var dist = Math.sqrt(dx*dx + dy*dy); | |
if (dist <= Math.abs(r2-r1)) return; // no valid tangents | |
// Rotation from x-axis | |
var angle1 = Math.atan2(dy,dx); | |
var angle2 = Math.acos((r1 - r2)/dist); | |
return [ | |
[ | |
[x1 + r1 * Math.cos(angle1 + angle2), y1 + r1 * Math.sin(angle1 + angle2)], | |
[x2 + r2 * Math.cos(angle1 + angle2), y2 + r2 * Math.sin(angle1 + angle2)] | |
], | |
[ | |
[x1 + r1 * Math.cos(angle1 - angle2), y1 + r1 * Math.sin(angle1 - angle2)], | |
[x2 + r2 * Math.cos(angle1 - angle2), y2 + r2 * Math.sin(angle1 - angle2)] | |
] | |
]; | |
} | |
var c1 = {x: 180, y: 150, r: 10}, | |
c2 = {x: 500, y: 200, r: 120}; | |
var color = d3.scale.category10(); | |
var svg = d3.select("svg"); | |
var circle = svg.selectAll(".circle") | |
.data([c1, c2]) | |
.enter().append("g") | |
.attr("class", "circle") | |
.attr("transform", function(d) { return "translate(" + d.x + "," + d.y + ")"; }) | |
.call(d3.behavior.drag() | |
.origin(function(d) { return d; }) | |
.on("dragstart", dragstarted) | |
.on("drag", dragged)); | |
circle.append("circle") | |
.attr("r", function(d) { return d.r; }); | |
var tangent = svg.selectAll(".line") | |
.data([ | |
function() { return outerTangent(c1.x, c1.y, +c1.r, c2.x, c2.y, +c2.r); }, | |
]) | |
.enter().insert("g", ".line") | |
.attr("class", "line") | |
.style("stroke", function(d, i) { return color(i); }); | |
tangent.append("line") | |
.attr("class", "line-1"); | |
tangent.append("line") | |
.attr("class", "line-2"); | |
update(); | |
function dragstarted(d) { | |
this.parentNode.appendChild(this); | |
} | |
function dragged(d) { | |
d3.select(this).attr("transform", "translate(" + (d.x = d3.event.x) + "," + (d.y = d3.event.y) + ")"); | |
update(); | |
} | |
function update() { | |
tangent.each(function(f) { | |
var c = f(); | |
if (c) { | |
d3.select(this).style("display", null); | |
tangent.select(".line-1") | |
.attr("x1", c[0][0][0]) | |
.attr("x2", c[0][1][0]) | |
.attr("y1", c[0][0][1]) | |
.attr("y2", c[0][1][1]); | |
tangent.select(".line-2") | |
.attr("x1", c[1][0][0]) | |
.attr("x2", c[1][1][0]) | |
.attr("y1", c[1][0][1]) | |
.attr("y2", c[1][1][1]); | |
} else { | |
d3.select(this).style("display", "none"); | |
} | |
}); | |
} | |
</script> |
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