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temporal contours #2254

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temporal contours #2254

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12 changes: 7 additions & 5 deletions src/marks/contour.js
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
import {blur2, contours, geoPath, max, min, nice, range, ticks, thresholdSturges} from "d3";
import {blur2, contours, geoPath, max, min, nice, range, ticks, thresholdSturges, scaleUtc} from "d3";
import {createChannels} from "../channel.js";
import {create} from "../context.js";
import {labelof, identity, arrayify, map} from "../options.js";
import {labelof, identity, arrayify, map, isTemporal} from "../options.js";
import {applyPosition} from "../projection.js";
import {applyChannelStyles, applyDirectStyles, applyIndirectStyles, applyTransform, styles} from "../style.js";
import {initializer} from "../transforms/basic.js";
Expand Down Expand Up @@ -115,7 +115,8 @@ function contourGeometry({thresholds, interval, ...options}) {
const {pixelSize: k, width: w = Math.round(Math.abs(dx) / k), height: h = Math.round(Math.abs(dy) / k)} = this;
const kx = w / dx;
const ky = h / dy;
const V = channels.value.value;
const temporal = isTemporal(channels.value.value);
const V = temporal && this.blur > 0 ? Float64Array.from(channels.value.value) : channels.value.value;
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Do we want to use coerceNumbers here whenever this.blur > 0, not just in the temporal case? I also wonder if we could provide a hint earlier when the value channel is declared to say that it must include numbers (at least in the this.blur > 0 case).

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I'd love to make contours work with categorical data, but I feel it would necessitate a completely different approach (we'd have to compute the contours for each of the categories on a boolean raster saying whether a pixel belongs to that category… something like that… with blurring to accomodate the "random-walk" interpolator).

const VV = []; // V per facet

// Interpolate the raster grid, as needed.
Expand Down Expand Up @@ -149,7 +150,7 @@ function contourGeometry({thresholds, interval, ...options}) {
if (this.blur > 0) for (const V of VV) blur2({data: V, width: w, height: h}, this.blur);

// Compute the contour thresholds.
const T = maybeTicks(thresholds, V, ...finiteExtent(VV));
const T = maybeTicks(thresholds, V, ...finiteExtent(VV), temporal);
if (T === null) throw new Error(`unsupported thresholds: ${thresholds}`);

// Compute the (maybe faceted) contours.
Expand Down Expand Up @@ -187,10 +188,11 @@ function contourGeometry({thresholds, interval, ...options}) {
// thresholds across facets. When an interval is used, note that the lowest
// threshold should be below (or equal) to the lowest value, or else some data
// will be missing.
function maybeTicks(thresholds, V, min, max) {
function maybeTicks(thresholds, V, min, max, temporal) {
if (typeof thresholds?.range === "function") return thresholds.range(thresholds.floor(min), max);
if (typeof thresholds === "function") thresholds = thresholds(V, min, max);
if (typeof thresholds !== "number") return arrayify(thresholds);
if (temporal) return scaleUtc().domain([min, max]).nice(thresholds).ticks(thresholds);
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@mbostock mbostock Nov 26, 2024 •
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I think we could use utcTickInterval here instead?

if (temporal) {
  thresholds = utcTickInterval(min, max, thresholds);
  return thresholds.range(thresholds.floor(min), max);
}

Maybe we could promote thresholds sooner and then you wouldn’t need to pass the temporal argument down here. Eh, this is fine.

const tz = ticks(...nice(min, max, thresholds), thresholds);
while (tz[tz.length - 1] >= max) tz.pop();
while (tz[1] < min) tz.shift();
Expand Down
72 changes: 72 additions & 0 deletions test/output/walmartsDateContours.html
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33 changes: 32 additions & 1 deletion test/plots/walmarts.ts
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
import * as Plot from "@observablehq/plot";
import * as d3 from "d3";
import {mesh} from "topojson-client";
import {feature, mesh} from "topojson-client";

export async function walmarts() {
const [walmarts, statemesh] = await Promise.all([
Expand Down Expand Up @@ -36,3 +36,34 @@ export async function walmarts() {
]
});
}

export async function walmartsDateContours() {
const [walmarts, [statemesh, nation]] = await Promise.all([
d3.tsv<any>("data/walmarts.tsv", d3.autoType),
d3.json<any>("data/us-counties-10m.json").then((us) => [
mesh(us, {
type: "GeometryCollection",
geometries: us.objects.states.geometries.filter((d) => d.id !== "02" && d.id !== "15")
}),
feature(us, us.objects.nation)
])
]);
return Plot.plot({
width: 960,
height: 600,
projection: "albers",
color: {legend: true, label: "Mean opening date"},
clip: nation,
marks: [
Plot.contour(walmarts, {
x: "longitude",
y: "latitude",
fill: "date",
interpolate: "random-walk",
blur: 5
}),
Plot.geo(statemesh, {strokeOpacity: 0.25}),
Plot.geo(nation, {strokeWidth: 1.5})
]
});
}