Published
Edited
Feb 23, 2021
text = fetch('https://raw.githubusercontent.com/visgl/deck.gl-data/master/website/scatterplot-data.txt').then(r => r.text())
lines = text.split('\n');
sampleLine = decodeSequence(lines[0])
sampleBbox = decodeBbox(lines[0].slice(0,20))
sampleBitmap = decodeBitmap(lines[0].slice(20))
{
var count = 0;
var result = [];
lines.forEach(function (l, i) {
var sequence = decodeSequence(l);
var bbox = decodeBbox(l.slice(0, 20));
var bitmap = decodeBitmap(l.slice(20));
for (var i = 0; i < bitmap.length; i++) {
if (bitmap[i] > 0) {
var point = [bbox[0] + (bbox[2] - bbox[0]) * sequence[i * 2], bbox[1] + (bbox[3] - bbox[1]) * sequence[i * 2 + 1], Number(bitmap[i])];
result.push(point);
count++;
}
}
})
return result
}
function decodeSequence(str) {
var seq = [];
var tokens = str.split(/([A-Z])/).map(function (v) {
return parseInt(v, 36);
});
for (var i = 0; i < tokens.length - 1; i += 2) {
seq.push(tokens[i] / Math.pow(2, tokens[i + 1] - 10));
}
return seq;
}
function decodeBbox(str) {
var multiplyer = Math.pow(10, COORDINATE_PRECISION);
return decodeNumberArr(str, 90, 32, 5).map(function (x) {
return x / multiplyer - 180;
});
}
function decodeNumberArr(str, b, shift, length) {
var result = [];
for (var j = 0; j < str.length; j += length) {
var token = str.slice(j, j + length);
result.push(decodeNumber(token, b, shift));
}
return result;
}
function decodeNumber(str, b, shift) {
var x = 0;
var p = 1;
for (var i = str.length; i--;) {
x += (str.charCodeAt(i) - shift) * p;
p *= b;
}
return x;
}
function decodeBitmap(str) {
var chunkSize = 4;
var match = '';
for (var i = 0; i < str.length; i++) {
var seg = (str.charCodeAt(i) - 32).toString(3);
while (seg.length < chunkSize) {
seg = "0".concat(seg);
}
match += seg;
}
return match;
}
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