chart = {
const path = d3.geoPath();
const svg = d3
.create("svg")
.attr("viewBox", wide ? [0, 0, width, height] : [0, 0, height, width])
.style("display", "block")
.style("margin", "0 -14px")
.style("width", "calc(100% + 28px)")
.style("height", "auto");
const g = svg
.append("g")
.attr(
"transform",
wide
? null
: `
rotate(90 ${width / 2},${height / 2})
translate(${(width - height) / 2},${(width - height) / 2})
`
)
.attr("stroke", "white")
.attr("stroke-width", 0.03);
for (const threshold of thresholds) {
g.append("path")
.attr("d", path(simplify(contours.contour(data.values, threshold))))
.attr("fill", color(threshold));
yield svg.node();
}
}
contours = d3.contours().size([width, height])
simplify = shape => {
const t = topojson.presimplify(topojson.topology({ foo: shape }));
return Object.assign(
{},
shape,
topojson.feature(topojson.simplify(t), t.objects.foo).geometry
);
}
complete = contours(data.values)
simplified = complete.map(simplify)
{
const [a, b] = [simplified, complete].map(s => s.map(d => d.coordinates).flat(3).length);
return md`**Number of points: ${(-100 + 100 * (a / b)).toFixed(1)}%**
(${a} vs. ${b}).`
}
{
const [a, b] = [simplified, complete].map(s => JSON.stringify(s).length);
return md`**Size in bytes: ${(-100 + 100 * (a / b)).toFixed(1)}%** (${a} vs. ${b}).`
}
width = data.width
height = data.height
wide = Generators.observe(notify => {
let wide;
function resized() {
let w = window.innerWidth > 640;
if (w !== wide) notify(wide = w);
}
resized();
window.addEventListener("resize", resized);
return () => window.removeEventListener("resize", resized);
})
color = d3.scaleSequential(interpolateTerrain).domain(d3.extent(data.values)).nice()
thresholds = color.ticks(20)
data = FileAttachment("volcano.json").json()
interpolateTerrain = {
const i0 = d3.interpolateHsvLong(d3.hsv(120, 1, 0.65), d3.hsv(60, 1, 0.90));
const i1 = d3.interpolateHsvLong(d3.hsv(60, 1, 0.90), d3.hsv(0, 0, 0.95));
return t => t < 0.5 ? i0(t * 2) : i1((t - 0.5) * 2);
}
d3 = require("d3@5", "d3-hsv@0.1")
topojson = require("topojson@3")
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