tweenPath = (data, fromIndex, toIndex, t, isClosed) => {
const m = dists[fromIndex].m + t * (dists[toIndex].m - dists[fromIndex].m);
const sd = dists[fromIndex].sd + t * (dists[toIndex].sd - dists[fromIndex].sd);
data.forEach((datum, i) => {
data[i] = createDatum(i, { m, sd });
});
const closer = isClosed ? " Z" : "";
return `${line(data)}${closer}`;
}