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Scale-Dependent Sampling
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license: gpl-3.0 |
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<!DOCTYPE html> | |
<meta charset="utf-8"> | |
<body> | |
<script src="//d3js.org/d3.v3.min.js"></script> | |
<script> | |
var width = 960, | |
height = 500, | |
graticulePrecision = 1; | |
var buffer, bufferContext = { | |
moveTo: function(x, y) { buffer.push([x, y]); }, | |
lineTo: function(x, y) { buffer.push([x, y]); }, | |
closePath: function() {} | |
}; | |
var projection = d3.geo.equirectangular() | |
.rotate([0, 0, 89]) | |
.translate([width / 2, height / 2]) | |
.scale(145) | |
.precision(.3) | |
.clipExtent([[-1, -1], [width + 1, height + 1]]); | |
var canvas = d3.select("body").append("canvas") | |
.attr("width", width) | |
.attr("height", height); | |
var context = canvas.node().getContext("2d"), | |
path = d3.geo.path().projection(projection).context(context), | |
graticule = d3.geo.graticule()(), | |
sphere = {type: "Sphere"}, | |
equator = {type: "LineString", coordinates: [[-180, 0], [-90, 0], [0, 0], [90, 0], [180, 0]]}; | |
animation(); | |
function animation() { | |
canvas.transition() | |
.duration(7500) | |
.tween("projection", function() { | |
var scale = d3.interpolate(145, 145 * 32), | |
translate = d3.interpolate([width / 2, height / 2], [1076, -6457]); | |
return function(t) { | |
projection.scale(scale(t)).translate(translate(t)); | |
render(); | |
}; | |
}) | |
.transition() | |
.duration(7500) | |
.tween("projection", function() { | |
var scale = d3.interpolate(145 * 32, 145), | |
translate = d3.interpolate([1076, -6457], [width / 2, height / 2]); | |
return function(t) { | |
projection.scale(scale(t)).translate(translate(t)); | |
render(); | |
}; | |
}) | |
.transition() | |
.duration(2500) | |
.each("end", animation); | |
} | |
function render() { | |
context.clearRect(0, 0, width, height); | |
if (d3.event) projection | |
.translate(d3.event.translate) | |
.scale(d3.event.scale); | |
context.strokeStyle = "#aaa"; | |
context.lineWidth = 1; | |
context.beginPath(); | |
path(graticule); | |
context.stroke(); | |
context.lineWidth = 2; | |
context.beginPath(); | |
path(sphere); | |
context.stroke(); | |
context.strokeStyle = "red"; | |
context.beginPath(); | |
path(equator); | |
context.stroke(); | |
// Override the path context to extract the resampled points. | |
buffer = []; | |
path.context(bufferContext); | |
path(equator); | |
buffer.forEach(function(d) { | |
context.beginPath(); | |
context.arc(d[0], d[1], 4.5, 0, 2 * Math.PI, false); | |
context.stroke(); | |
}); | |
path.context(context); | |
context.restore(); | |
} | |
</script> |
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