Published
Edited
Apr 18, 2021
1 star
MBP = {
let perimeter = [],
remainingIndices = d3.range(0, border.length),
lastBearing,
distance = 0;
//Starting point
perimeter.push(border[d3.maxIndex(border, p => p[1])]); // most northerly point
lastBearing = 90; // East
//Subsequent points
while (
!arrEq(perimeter[0], perimeter[perimeter.length - 1]) || //stop when back at first point
perimeter.length == 1
) {
yield Promises.tick(200, {
type: "LineString",
coordinates: perimeter,
distance
});
//bearings to candidate points
const bearings = remainingIndices.map(i =>
calculateBearing(perimeter[perimeter.length - 1], border[i])
);
//selection of minimal acceptable bearing
const nextIndex = d3.minIndex(bearings, b => {
if (b > lastBearing) {
return b - lastBearing;
} else if (b > lastBearing - 90) {
//great circle bearing is relative
return b - lastBearing;
} else if (b < lastBearing - 180) {
return b + 360 - lastBearing;
} else {
return NaN;
}
});
lastBearing = bearings[nextIndex];
perimeter.push(border[nextIndex]);
distance += calculateDistance(
perimeter[perimeter.length - 2],
perimeter[perimeter.length - 1]
);
}
yield { type: "Polygon", coordinates: [perimeter], distance };
}
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.
