javascript
/
three.js
mirror of https://github.com/tazdij/three.js.git


			
				
					
						
						
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							<!doctype html>
<html>
<meta charset="utf-8">
<head>
<title>gpw data viewer</title>
<style>
canvas {
  max-width: calc(100% - 16px);
}
</style>
</head>
<body>
<canvas></canvas>
</body>
<script type="module">

async function loadFile(url) {
  const req = await fetch(url);
  return req.text();
}

function parseData(text) {
  const data = [];
  const settings = {data};
  let max;
  let min;
  // split into lines
  text.split('\n').forEach((line) => {
    // split the line by whitespace
    const parts = line.trim().split(/\s+/);
    if (parts.length === 2) {
      // only 2 parts, must be a key/value pair
      settings[parts[0]] = parseFloat(parts[1]);
    } else if (parts.length > 2) {
      // more than 2 parts, must be data
      const values = parts.map((v) => {
        const value = parseFloat(v);
        if (value === settings.NODATA_value) {
          return undefined;
        }
        max = Math.max(max === undefined ? value : max, value);
        min = Math.min(min === undefined ? value : min, value);
        return value;
      });
      data.push(values);
    }
  });
  return Object.assign(settings, {min, max});
}

function drawData(file) {
  const {min, max, ncols, nrows, data} = file;
  const range = max - min;
  const ctx = document.querySelector('canvas').getContext('2d');
  // make the canvas the same size as the data
  ctx.canvas.width = ncols;
  ctx.canvas.height = nrows;
  // but display it double size so it's not too small
  ctx.canvas.style.width = px(ncols * 2);
  // fill the canvas to dark gray
  ctx.fillStyle = '#444';
  ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
  // draw each data point
  data.forEach((row, latNdx) => {
    row.forEach((value, lonNdx) => {
      if (value === undefined) {
        return;
      }
      const amount = (value - min) / range;
      const hue = 1;
      const saturation = 1;
      const lightness = amount;
      ctx.fillStyle = hsl(hue, saturation, lightness);
      ctx.fillRect(lonNdx, latNdx, 1, 1);
    });
  });
}

function px(v) {
  return `${v | 0}px`;
}

function hsl(h, s, l) {
  return `hsl(${h * 360 | 0},${s * 100 | 0}%,${l * 100 | 0}%)`;
}

loadFile('resources/data/gpw/gpw_v4_basic_demographic_characteristics_rev10_a000_014mt_2010_cntm_1_deg.asc')
  .then(parseData)
  .then(drawData);

</script>
</html>