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Oct 6, 2024
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initialProjection = d3.geoIdentity().translate([rawData.gridWidth / 2, rawData.gridHeight / 2]);
// ↳ Note that this rectangular grid could also be treated as an equirectangular projection.
// initialProjection = d3.geoEquirectangular().translate([rawData.gridWidth / 2, rawData.gridHeight / 2]).scale(57.35).reflectY(true);
contours = thresholds =>
d3.contours()
.size([rawData.gridWidth, rawData.gridHeight])
.thresholds(thresholds)(rawData.data);
function projectContour(contour) {
return {
type: contour.type,
value: contour.value,
coordinates: contour.coordinates.map(polygon =>
polygon.map(line =>
line.map(point => { return initialProjection.invert(point); })
)
)
};
}
projectedContours = thresholds => contours(thresholds).map(projectContour);
projectedContours([0])
projections = [
{name: "Aitoff", value: d3.geoAitoff().scale(140)},
{name: "August", value: d3.geoAugust()},
{name: "Bertin’s 1953", value: d3.geoBertin1953()},
{name: "Ginzburg V", value: d3.geoGinzburg5()},
{name: "Equirectangular", value: d3.geoEquirectangular().translate([width/2,height/2-100]).scale(150)},
{name: "Mercator", value: d3.geoMercator().translate([width/2,height/2-30]).scale(153.5)},
{name: "Miller", value: d3.geoMiller().translate([width/2,height/2-10]).scale(153.5)},
]
fileMap = [
{year: "1900", file: FileAttachment("IGRF-13_declination_1900.csv") },
{year: "2020", file: FileAttachment("IGRF-13_declination_2020.csv") },
{year: "2025", file: FileAttachment("IGRF-13_declination_2025.csv") },
]
topojson = require("topojson-client@3")
d3 = require("d3@5", "d3-geo-projection@3")
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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.
