{
const projection = d3.geoMercator().fitExtent(
[
[0, 0],
[width, 650]
],
contours[0]
);
const path = d3.geoPath(projection);
const svg = DOM.svg(width, 650);
d3.select(svg)
.append("g")
.attr("stroke", "#fff")
.attr("stroke-width", 0.5)
.selectAll()
.data(contours)
.join("path")
.attr("fill", (d) => color(d.value))
.attr("d", path);
return svg;
}
n = 152 // guessed from points.length
m = 106
contours = d3
.contours()
.thresholds(20)
.size([n, m])(grid.Z.map((d) => d))
.map(project) // reproject to WGS84
projection = ([x, y]) => {
const x0 = clamp(Math.floor(x), 0, n - 1),
dx = x - x0;
const x1 = clamp(Math.ceil(x), 0, n - 1),
rx = dx / (x1 - x);
const y0 = clamp(Math.floor(y), 0, m - 1),
dy = y - y0;
const y1 = clamp(Math.ceil(y), 0, m - 1),
ry = dy / (y1 - y);
// bilinear interpolation
const qx = i(
i(grid.X[x0 + n * y0], grid.X[x1 + n * y0], rx),
i(grid.X[x0 + n * y1], grid.X[x1 + n * y1], rx),
ry
);
const qy = i(
i(grid.Y[x0 + n * y0], grid.Y[x0 + n * y1], ry),
i(grid.Y[x1 + n * y0], grid.Y[x1 + n * y1], ry),
rx
);
return [qx, qy];
// linear interpolation
function i(a, b, r) {
return a === b ? a : (a + b * r) / (r + 1);
}
function clamp(x, lo, hi) {
return x < lo ? lo : x > hi ? hi : x;
}
}
color = d3
.scaleSequential(d3.interpolateMagma)
.domain(d3.extent(contours, (d) => d.value))
function project(d) {
d = {
...d,
coordinates: d.coordinates.map((poly) =>
poly.map((ring) => ring.map(projection).reverse())
)
};
return d;
}
points = FileAttachment("data-issue-64@1.json")
.json()
.then((d) => d.data.data.json)
grid = ({
X: points.map((d) => d[0]),
Y: points.map((d) => d[1]),
Z: points.map((d) => d[2])
})
Plot.carto({
height: 500,
marks: [
Plot.points(points, {
lonLat: (d) => d,
fill: (d) => d[2] || 20, // in orange, the null data
r: 1
})
]
})
import { Plot } from "@fil/plot-carto-0-5"
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