contours = d3.contours().size([n, m]).smooth(true).thresholds(20)
contoursGeo = contours.contour(values, 0.01)
m = image.naturalHeight
n = image.naturalWidth
// https://aviationweather.gov/wafs/ [-75.940536, -179.983902], [75.940536, 179.983902]
image = Object.assign(
await FileAttachment("20231228_12_F06_wafs_301_wind_m.png").image(),
{ style: "max-height: 33px; display: block;" }
)
// https://stackoverflow.com/questions/2103924/mercator-longitude-and-latitude-calculations-to-x-and-y-on-a-cropped-map-of-the/10401734#10401734
function pixelToGeo(point) {
let mapWidth = 900;
let mapHeight = 600;
let mapLonLeft = -180;
let mapLonRight = 180;
let mapLonDelta = mapLonRight - mapLonLeft;
let mapLatBottom = 180;
let mapLatBottomRadian = (mapLatBottom * Math.PI) / 180;
let tx = point[0];
let ty = point[1];
let worldMapRadius = ((mapWidth / mapLonDelta) * 360) / (2 * Math.PI);
// Not sure what's happening here... I think equator offset but that's not important here since equator is in the center of the image...
let mapOffsetY =
(worldMapRadius / 2) *
Math.log(
(1 + Math.sin(mapLatBottomRadian)) / (1 - Math.sin(mapLatBottomRadian))
);
let equatorY = mapHeight + -300;
let a = (equatorY - ty) / worldMapRadius;
let lat = (180 / Math.PI) * (2 * Math.atan(Math.exp(a)) - Math.PI / 2);
let lon = mapLonLeft + (tx / mapWidth) * mapLonDelta;
return [lon, lat];
}
land = topojson.feature(world, world.objects.land)
world = FileAttachment("land-50m.json").json()
d3 = require("d3@7.6.0/dist/d3.min.js") // d3.blur was introduced in d3-array@3.2 and d3@7.6
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