function geoGraticule() {
const { abs, ceil } = Math;
const epsilon = 1e-6;
const { range } = d3;
function graticuleX(y0, y1, dy) {
var y = range(y0, y1 - epsilon, dy).concat(y1);
return function(x) { return y.map(function(y) { return [x, y]; }); };
}
function graticuleY(x0, x1, dx) {
var x = range(x0, x1 - epsilon, dx).concat(x1);
return function(y) { return x.map(function(x) { return [x, y]; }); };
}
var x1, x0, X1, X0,
y1, y0, Y1, Y0,
dx = 10, dy = dx, DX = 90, DY = 360,
x, y, X, Y,
precision = 2.5;
function graticule() {
return {type: "MultiLineString", coordinates: lines()};
}
function lines() {
return range(ceil(X0 / DX) * DX, X1, DX).map(X)
.concat(range(ceil(Y0 / DY) * DY, Y1, DY).map(Y))
.concat(range(ceil(x0 / dx) * dx, x1, dx).filter(function(x) { return abs(x % DX) > epsilon; }).map(x))
.concat(range(ceil(y0 / dy) * dy, y1, dy).filter(function(y) { return abs(y % DY) > epsilon; }).map(y));
}
graticule.lines = function() {
return lines().map(function(coordinates) { return {type: "LineString", coordinates: coordinates}; });
};
graticule.outline = function() {
return {
type: "Polygon",
coordinates: [
X(X0).concat(
Y(Y1).slice(1),
X(X1).reverse().slice(1),
Y(Y0).reverse().slice(1))
]
};
};
graticule.extent = function(_) {
if (!arguments.length) return graticule.extentMinor();
return graticule.extentMajor(_).extentMinor(_);
};
graticule.extentMajor = function(_) {
if (!arguments.length) return [[X0, Y0], [X1, Y1]];
X0 = +_[0][0], X1 = +_[1][0];
Y0 = +_[0][1], Y1 = +_[1][1];
if (X0 > X1) _ = X0, X0 = X1, X1 = _;
if (Y0 > Y1) _ = Y0, Y0 = Y1, Y1 = _;
return graticule.precision(precision);
};
graticule.extentMinor = function(_) {
if (!arguments.length) return [[x0, y0], [x1, y1]];
x0 = +_[0][0], x1 = +_[1][0];
y0 = +_[0][1], y1 = +_[1][1];
if (x0 > x1) _ = x0, x0 = x1, x1 = _;
if (y0 > y1) _ = y0, y0 = y1, y1 = _;
return graticule.precision(precision);
};
graticule.step = function(_) {
if (!arguments.length) return graticule.stepMinor();
return graticule.stepMajor(_).stepMinor(_);
};
graticule.stepMajor = function(_) {
if (!arguments.length) return [DX, DY];
DX = +_[0], DY = +_[1];
return graticule;
};
graticule.stepMinor = function(_) {
if (!arguments.length) return [dx, dy];
dx = +_[0], dy = +_[1];
return graticule;
};
graticule.precision = function(_) {
if (!arguments.length) return precision;
precision = +_;
x = graticuleX(y0, y1, precision);
y = graticuleY(x0, x1, precision);
X = graticuleX(Y0, Y1, precision);
Y = graticuleY(X0, X1, precision);
return graticule;
};
return graticule
.extentMajor([[-180, -90 + epsilon], [180, 90 - epsilon]])
.extentMinor([[-180, -80 - epsilon], [180, 80 + epsilon]]);
}