chart = {
const context = DOM.context2d(width, height);
const path = d3.geoPath(projection, context);
function render(land) {
context.clearRect(0, 0, width, height);
context.beginPath(), path(sphere), context.fillStyle = "#058", context.fill();
context.beginPath(), path(land), context.fillStyle = "#040", context.fill();
context.beginPath(), path(sphere), context.stroke();
}
return d3.select(context.canvas)
.call(drag(projection)
.on("drag.render", () => render(land110))
.on("end.render", () => render(land50)))
.call(() => render(land50))
.node();
}
viewof projectionName = html`<select>
<option value="geoOrthographic">Orthographic</option>
<option value="geoMercator">Mercator</option>
<option value="geoNaturalEarth1">Natural Earth</option>
<option value="geoEquirectangular">Plate Carrée</option>
<option value="geoAzimuthalEqualArea">Azimuthal</option>
<option value="geoAlbers">Albers</option>
<option value="geoConicEqualArea">Conic</option>
<option value="geoGnomonic">Gnomonic</option>
<option value="geoTransverseMercator">TransverseMercator</option>
<option value="geoAzimuthalEquidistant">Azimuthal, not equal area</option>
<option value="geoEqualEarth">Equal Earth</option>
<option value="geoConicEquidistant">Conic, not equal area<option/>
<option value="geoStereographic">Stereographic</option>
<select/>`
function drag(projection) {
let v0, q0, r0, a0, l;
function pointer(event, that) {
const t = d3.pointers(event, that);
if (t.length !== l) {
l = t.length;
if (l > 1) a0 = Math.atan2(t[1][1] - t[0][1], t[1][0] - t[0][0]);
dragstarted.apply(that, [event, that]);
}
// For multitouch, average positions and compute rotation.
if (l > 1) {
const x = d3.mean(t, p => p[0]);
const y = d3.mean(t, p => p[1]);
const a = Math.atan2(t[1][1] - t[0][1], t[1][0] - t[0][0]);
return [x, y, a];
}
return t[0];
}
function dragstarted(event) {
v0 = versor.cartesian(projection.invert(pointer(event, this)));
q0 = versor(r0 = projection.rotate());
}
function dragged(event) {
const p = pointer(event, this);
const v1 = versor.cartesian(projection.rotate(r0).invert(p));
const delta = versor.delta(v0, v1);
let q1 = versor.multiply(q0, delta);
// For multitouch, compose with a rotation around the axis.
if (p[2]) {
const d = (p[2] - a0) / 2;
const s = -Math.sin(d);
const c = Math.sign(Math.cos(d));
q1 = versor.multiply([Math.sqrt(1 - s * s), 0, 0, c * s], q1);
}
projection.rotate(versor.rotation(q1));
// In vicinity of the antipode (unstable) of q0, restart.
if (delta[0] < 0.7) dragstarted.apply(this, [event, this]);
}
return d3.drag()
.on("start", dragstarted)
.on("drag", dragged);
}
projection = d3[projectionName]().precision(0.1)
height = {
const [[x0, y0], [x1, y1]] = d3.geoPath(projection.fitWidth(width, sphere)).bounds(sphere);
const dy = Math.ceil(y1 - y0), l = Math.min(Math.ceil(x1 - x0), dy);
projection.scale(projection.scale() * (l - 1) / l).precision(0.2);
return dy;
}
sphere = ({type: "Sphere"})
land50 = FileAttachment("land-50m.json").json().then(world => topojson.feature(world, world.objects.land))
land110 = FileAttachment("land-110m.json").json().then(world => topojson.feature(world, world.objects.land))
versor = require("versor@0.0.3")
topojson = require("topojson-client@3")
d3 = require("d3@7", "d3-geo-projection@4")
Purpose-built for displays of data
Observable is your go-to platform for exploring data and creating expressive data visualizations. Use reactive JavaScript notebooks for prototyping and a collaborative canvas for visual data exploration and dashboard creation.
