Closed beuan closed 4 years ago
Not an answer to your question, but here's a modernized version, with a clip-angle of 145°: https://observablehq.com/@fil/two-point-equidistant
I have updated https://observablehq.com/@fil/two-point-equidistant with polygon clipping. The polygon in question is quite simple: it's just a rectangle that runs around the antipodes of the two centers. It covers 99.9996% of the globe ;)
Oh and, if you want spherical ellipses, we got it covered too: https://observablehq.com/@fil/spherical-ellipses
(turns out they're not needed for this projection since we want the "largest" ellipse we can get, and that's our simple polygon).
Cool! I will have to wait for the next release, but how can I add this clipping polygon to my call?
return d3.geoTwoPointEquidistant([lon1, lat1],[lon2, lat2])
.clipAngle(105);
Thanks! 🙏🏻
The technique works with the current releases (d3-geo@1, d3-geo-projection@2 and d3-geo-polygon@1). The relevant call is
projection.preclip(d3.geoClipPolygon(ellipse));
where ellipse
is a GeoJSON polygon that goes “around” the antipodes of the two centers a and b (in the rotation that puts them symmetrically around [0,0] on the equator):
const eps = 1e-3, u = (d3.geoDistance(a, b) / 2) * degrees + eps,
ellipse = {
type: "Polygon",
coordinates: [[
[180 - u, eps],
[180 - u, -eps],
[-180 + u, -eps],
[-180 + u, eps],
[180 - u, eps]
]]
};
Sweet! It works like a charm. Thank you for your help, @Fil! 🙏🏻
Is there any short term plan to fix artifacts when showing the whole world with the two-point equidistant projection? https://github.com/d3/d3-geo-projection/blob/aa9e19e0da32c67f875a85ff0c6d8ce83a186e22/src/twoPointEquidistant.js#L4-L6