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92 lines
2.3 KiB
92 lines
2.3 KiB
<!doctype html>
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<html>
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<meta charset="utf-8">
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<head>
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<title>gpw data viewer</title>
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<style>
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canvas {
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max-width: calc(100% - 16px);
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}
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</style>
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</head>
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<body>
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<canvas></canvas>
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</body>
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<script type="module">
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async function loadFile(url) {
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const req = await fetch(url);
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return req.text();
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}
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function parseData(text) {
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const data = [];
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const settings = {data};
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let max;
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let min;
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// split into lines
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text.split('\n').forEach((line) => {
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// split the line by whitespace
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const parts = line.trim().split(/\s+/);
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if (parts.length === 2) {
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// only 2 parts, must be a key/value pair
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settings[parts[0]] = parseFloat(parts[1]);
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} else if (parts.length > 2) {
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// more than 2 parts, must be data
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const values = parts.map((v) => {
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const value = parseFloat(v);
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if (value === settings.NODATA_value) {
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return undefined;
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}
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max = Math.max(max === undefined ? value : max, value);
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min = Math.min(min === undefined ? value : min, value);
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return value;
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});
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data.push(values);
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}
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});
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return Object.assign(settings, {min, max});
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}
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function drawData(file) {
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const {min, max, ncols, nrows, data} = file;
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const range = max - min;
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const ctx = document.querySelector('canvas').getContext('2d');
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// make the canvas the same size as the data
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ctx.canvas.width = ncols;
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ctx.canvas.height = nrows;
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// but display it double size so it's not too small
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ctx.canvas.style.width = px(ncols * 2);
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// fill the canvas to dark gray
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ctx.fillStyle = '#444';
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ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
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// draw each data point
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data.forEach((row, latNdx) => {
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row.forEach((value, lonNdx) => {
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if (value === undefined) {
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return;
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}
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const amount = (value - min) / range;
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const hue = 1;
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const saturation = 1;
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const lightness = amount;
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ctx.fillStyle = hsl(hue, saturation, lightness);
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ctx.fillRect(lonNdx, latNdx, 1, 1);
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});
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});
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}
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function px(v) {
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return `${v | 0}px`;
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}
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function hsl(h, s, l) {
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return `hsl(${h * 360 | 0},${s * 100 | 0}%,${l * 100 | 0}%)`;
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}
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loadFile('resources/data/gpw/gpw_v4_basic_demographic_characteristics_rev10_a000_014mt_2010_cntm_1_deg.asc')
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.then(parseData)
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.then(drawData);
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</script>
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</html>
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