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selimnairb/hrrr_legend_test.html

Created June 3, 2021 19:46
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Use HTML5 Canvas API to draw a legend for NOAA High-Resolution Rapid Refresh (HRRR) simulated radar reflectivity data (https://rapidrefresh.noaa.gov/hrrr/)
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hrrr_legend_test.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>HRRR legend test</title>
<!-- Use HTML5 Canvas API to draw a legend for NOAA High-Resolution Rapid Refresh
(HRRR) simulated radar reflectivity data (https://rapidrefresh.noaa.gov/hrrr/)
-->
</head>
<body>
<canvas id="canvas" width=548></canvas>
<script>
// HRRR color ramp from: https://mesonet.agron.iastate.edu/GIS/rasters.php?rid=2
let HRRR_ramp = [
{"label": "ND", "color": "#000000"},
{"label": "-32", "color": "#85718f"},
{"label": "-31.5", "color": "#85728f"},
{"label": "-31", "color": "#86738d"},
{"label": "-30.5", "color": "#87758b"},
{"label": "-30", "color": "#87768b"},
{"label": "-29.5", "color": "#887789"},
{"label": "-29", "color": "#897987"},
{"label": "-28.5", "color": "#897a87"},
{"label": "-28", "color": "#8a7b85"},
{"label": "-27.5", "color": "#8b7d84"},
{"label": "-27", "color": "#8b7e84"},
{"label": "-26.5", "color": "#8c7f82"},
{"label": "-26", "color": "#8d8180"},
{"label": "-25.5", "color": "#8d8280"},
{"label": "-25", "color": "#8e837e"},
{"label": "-24.5", "color": "#8f847c"},
{"label": "-24", "color": "#8f857c"},
{"label": "-23.5", "color": "#90877b"},
{"label": "-23", "color": "#918879"},
{"label": "-22.5", "color": "#918979"},
{"label": "-22", "color": "#928b77"},
{"label": "-21.5", "color": "#938d75"},
{"label": "-21", "color": "#969153"},
{"label": "-20.5", "color": "#989457"},
{"label": "-20", "color": "#9b975b"},
{"label": "-19.5", "color": "#9d9a60"},
{"label": "-19", "color": "#a09d64"},
{"label": "-18.5", "color": "#a3a068"},
{"label": "-18", "color": "#a5a36d"},
{"label": "-17.5", "color": "#a8a671"},
{"label": "-17", "color": "#aaa976"},
{"label": "-16.5", "color": "#adac7a"},
{"label": "-16", "color": "#b0af7e"},
{"label": "-15.5", "color": "#b2b283"},
{"label": "-15", "color": "#b7b88c"},
{"label": "-14.5", "color": "#babb90"},
{"label": "-14", "color": "#bdbe94"},
{"label": "-13.5", "color": "#bfc199"},
{"label": "-13", "color": "#c2c49d"},
{"label": "-12.5", "color": "#c4c7a2"},
{"label": "-12", "color": "#c7caa6"},
{"label": "-11.5", "color": "#cacdaa"},
{"label": "-11", "color": "#ccd0af"},
{"label": "-10.5", "color": "#d2d4b4"},
{"label": "-10", "color": "#cfd2b4"},
{"label": "-9.5", "color": "#c9ccb4"},
{"label": "-9", "color": "#c6c9b4"},
{"label": "-8.5", "color": "#c3c7b4"},
{"label": "-8", "color": "#c0c4b4"},
{"label": "-7.5", "color": "#bdc1b4"},
{"label": "-7", "color": "#b9beb4"},
{"label": "-6.5", "color": "#b6bbb4"},
{"label": "-6", "color": "#b3b9b4"},
{"label": "-5.5", "color": "#b0b6b4"},
{"label": "-5", "color": "#adb3b4"},
{"label": "-4.5", "color": "#aab0b4"},
{"label": "-4", "color": "#a4abb4"},
{"label": "-3.5", "color": "#a0a8b4"},
{"label": "-3", "color": "#9da5b4"},
{"label": "-2.5", "color": "#9aa2b4"},
{"label": "-2", "color": "#97a0b4"},
{"label": "-1.5", "color": "#949db4"},
{"label": "-1", "color": "#919ab4"},
{"label": "-0.5", "color": "#949bb5"},
{"label": "0", "color": "#9098b4"},
{"label": "0.5", "color": "#8c95b3"},
{"label": "1", "color": "#8892b2"},
{"label": "1.5", "color": "#808cb0"},
{"label": "2", "color": "#7c89af"},
{"label": "2.5", "color": "#7886ae"},
{"label": "3", "color": "#7483ac"},
{"label": "3.5", "color": "#7080ab"},
{"label": "4", "color": "#6c7daa"},
{"label": "4.5", "color": "#6779a9"},
{"label": "5", "color": "#6376a8"},
{"label": "5.5", "color": "#5f73a7"},
{"label": "6", "color": "#5b70a6"},
{"label": "6.5", "color": "#576da4"},
{"label": "7", "color": "#4f67a2"},
{"label": "7.5", "color": "#4b64a1"},
{"label": "8", "color": "#4761a0"},
{"label": "8.5", "color": "#435e9f"},
{"label": "9", "color": "#415b9e"},
{"label": "9.5", "color": "#4361a2"},
{"label": "10", "color": "#4568a6"},
{"label": "10.5", "color": "#486faa"},
{"label": "11", "color": "#4a76ae"},
{"label": "11.5", "color": "#4d7db2"},
{"label": "12", "color": "#4f84b6"},
{"label": "12.5", "color": "#518bbb"},
{"label": "13", "color": "#5699c3"},
{"label": "13.5", "color": "#599fc7"},
{"label": "14", "color": "#5ba6cb"},
{"label": "14.5", "color": "#5eadcf"},
{"label": "15", "color": "#60b4d4"},
{"label": "15.5", "color": "#62bbd8"},
{"label": "16", "color": "#65c2dc"},
{"label": "16.5", "color": "#67c9e0"},
{"label": "17", "color": "#6ad0e4"},
{"label": "17.5", "color": "#6fd6e8"},
{"label": "18", "color": "#68d6d7"},
{"label": "18.5", "color": "#59d6b3"},
{"label": "19", "color": "#52d6a2"},
{"label": "19.5", "color": "#4bd690"},
{"label": "20", "color": "#43d67e"},
{"label": "20.5", "color": "#3cd66d"},
{"label": "21", "color": "#35d65b"},
{"label": "21.5", "color": "#11d518"},
{"label": "22", "color": "#11d117"},
{"label": "22.5", "color": "#10cd17"},
{"label": "23", "color": "#10c816"},
{"label": "23.5", "color": "#10c416"},
{"label": "24", "color": "#0fbc15"},
{"label": "24.5", "color": "#0fb714"},
{"label": "25", "color": "#0eb314"},
{"label": "25.5", "color": "#0eaf13"},
{"label": "26", "color": "#0eab13"},
{"label": "26.5", "color": "#0da612"},
{"label": "27", "color": "#0da212"},
{"label": "27.5", "color": "#0d9e11"},
{"label": "28", "color": "#0c9911"},
{"label": "28.5", "color": "#0c9510"},
{"label": "29", "color": "#0c9110"},
{"label": "29.5", "color": "#0b880f"},
{"label": "30", "color": "#0b840e"},
{"label": "30.5", "color": "#0a800e"},
{"label": "31", "color": "#0a7c0d"},
{"label": "31.5", "color": "#0a770d"},
{"label": "32", "color": "#09730c"},
{"label": "32.5", "color": "#096f0c"},
{"label": "33", "color": "#096b0b"},
{"label": "33.5", "color": "#08660b"},
{"label": "34", "color": "#08620a"},
{"label": "34.5", "color": "#095e09"},
{"label": "35", "color": "#327308"},
{"label": "35.5", "color": "#467d08"},
{"label": "36", "color": "#5b8807"},
{"label": "36.5", "color": "#6f9207"},
{"label": "37", "color": "#849d06"},
{"label": "37.5", "color": "#98a806"},
{"label": "38", "color": "#adb205"},
{"label": "38.5", "color": "#c1bd05"},
{"label": "39", "color": "#d6c704"},
{"label": "39.5", "color": "#ead204"},
{"label": "40", "color": "#ffe200"},
{"label": "40.5", "color": "#ffd800"},
{"label": "41", "color": "#ffd300"},
{"label": "41.5", "color": "#ffce00"},
{"label": "42", "color": "#ffc900"},
{"label": "42.5", "color": "#ffc400"},
{"label": "43", "color": "#ffc000"},
{"label": "43.5", "color": "#ffbb00"},
{"label": "44", "color": "#ffb600"},
{"label": "44.5", "color": "#ffb100"},
{"label": "45", "color": "#ffac00"},
{"label": "45.5", "color": "#ffa700"},
{"label": "46", "color": "#ffa200"},
{"label": "46.5", "color": "#ff9900"},
{"label": "47", "color": "#ff9400"},
{"label": "47.5", "color": "#ff8f00"},
{"label": "48", "color": "#ff8a00"},
{"label": "48.5", "color": "#ff8500"},
{"label": "49", "color": "#ff8000"},
{"label": "49.5", "color": "#ff0000"},
{"label": "50", "color": "#f80000"},
{"label": "50.5", "color": "#f10000"},
{"label": "51", "color": "#ea0000"},
{"label": "51.5", "color": "#e30000"},
{"label": "52", "color": "#d50000"},
{"label": "52.5", "color": "#cd0000"},
{"label": "53", "color": "#c60000"},
{"label": "53.5", "color": "#bf0000"},
{"label": "54", "color": "#b80000"},
{"label": "54.5", "color": "#b10000"},
{"label": "55", "color": "#aa0000"},
{"label": "55.5", "color": "#a30000"},
{"label": "56", "color": "#9b0000"},
{"label": "56.5", "color": "#940000"},
{"label": "57", "color": "#8d0000"},
{"label": "57.5", "color": "#7f0000"},
{"label": "58", "color": "#780000"},
{"label": "58.5", "color": "#710000"},
{"label": "59", "color": "#ffffff"},
{"label": "59.5", "color": "#fff5ff"},
{"label": "60", "color": "#ffeaff"},
{"label": "60.5", "color": "#ffdfff"},
{"label": "61", "color": "#ffd4ff"},
{"label": "61.5", "color": "#ffc9ff"},
{"label": "62", "color": "#ffbeff"},
{"label": "62.5", "color": "#ffb3ff"},
{"label": "63", "color": "#ff9dff"},
{"label": "63.5", "color": "#ff92ff"},
{"label": "64", "color": "#ff75ff"},
{"label": "64.5", "color": "#fc6bfd"},
{"label": "65", "color": "#f960fa"},
{"label": "65.5", "color": "#f656f7"},
{"label": "66", "color": "#f34bf4"},
{"label": "66.5", "color": "#f040f1"},
{"label": "67", "color": "#ed36ef"},
{"label": "67.5", "color": "#ea2bec"},
{"label": "68", "color": "#e720e9"},
{"label": "68.5", "color": "#e10be3"},
{"label": "69", "color": "#b200ff"},
{"label": "69.5", "color": "#ac00fc"},
{"label": "70", "color": "#a400f7"},
{"label": "70.5", "color": "#9b00f4"},
{"label": "71", "color": "#9300ef"},
{"label": "71.5", "color": "#8800ea"},
{"label": "72", "color": "#8300e8"},
{"label": "72.5", "color": "#7900e2"},
{"label": "73", "color": "#7200dd"},
{"label": "73.5", "color": "#6900db"},
{"label": "74", "color": "#05ecf0"},
{"label": "74.5", "color": "#05ebf0"},
{"label": "75", "color": "#05eaf0"},
{"label": "75.5", "color": "#05dde0"},
{"label": "76", "color": "#05dce0"},
{"label": "76.5", "color": "#05dbe0"},
{"label": "77", "color": "#05cdd0"},
{"label": "77.5", "color": "#05ccd0"},
{"label": "78", "color": "#04bdc0"},
{"label": "78.5", "color": "#04bcc0"},
{"label": "79", "color": "#04bbc0"},
{"label": "79.5", "color": "#04aeb0"},
{"label": "80", "color": "#04adb0"},
{"label": "80.5", "color": "#049ea0"},
{"label": "81", "color": "#049da0"},
{"label": "81.5", "color": "#049ca0"},
{"label": "82", "color": "#038e90"},
{"label": "82.5", "color": "#038d90"},
{"label": "83", "color": "#038c90"},
{"label": "83.5", "color": "#037e80"},
{"label": "84", "color": "#037d80"},
{"label": "84.5", "color": "#036f70"},
{"label": "85", "color": "#036e70"},
{"label": "85.5", "color": "#036d70"},
{"label": "86", "color": "#025f60"},
{"label": "86.5", "color": "#025e60"},
{"label": "87", "color": "#024f50"},
{"label": "87.5", "color": "#024e50"},
{"label": "88", "color": "#024d50"},
{"label": "88.5", "color": "#023f40"},
{"label": "89", "color": "#023e40"},
{"label": "89.5", "color": "#023d40"},
{"label": "90", "color": "#013030"},
{"label": "90.5", "color": "#012f30"},
{"label": "91", "color": "#012020"},
{"label": "91.5", "color": "#011f20"},
{"label": "92", "color": "#011e20"},
{"label": "92.5", "color": "#3a67b5"},
{"label": "93", "color": "#3a66b5"},
{"label": "93.5", "color": "#3a65b5"},
{"label": "94", "color": "#3a64b5"},
{"label": "94.5", "color": "#3a63b5"},
{"label": "95", "color": "#3a62b5"},
];
// Support for HiDPI displays
// Adapted from: https://www.html5rocks.com/en/tutorials/canvas/hidpi/
// and: https://www.kirupa.com/canvas/canvas_high_dpi_retina.htm
function setupCanvas(canvas) {
// Get the device pixel ratio, falling back to 1.
var dpr = window.devicePixelRatio || 1;
// Get the size of the canvas in CSS pixels.
var rect = canvas.getBoundingClientRect();
// Give the canvas pixel dimensions of their CSS
// size * the device pixel ratio.
canvas.width = rect.width * dpr;
canvas.height = rect.height * dpr;
var ctx = canvas.getContext('2d');
// Scale all drawing operations by the dpr, so you
// don't have to worry about the difference.
ctx.scale(dpr, dpr);
// scale everything down using CSS
canvas.style.width = rect.width + 'px';
canvas.style.height = rect.height + 'px';
return ctx;
}
const leftMargin = 10;
const topMargin = 10;
const rampWidth = 512;
const rampHeight = 24;
const ticYstop = 40;
const labelYstart = 48;
const firstLabelXoffset = 4
const labelXoffset = 8;
const endTicXoffset = 1;
const ctx = setupCanvas(document.querySelector('canvas'));
ctx.font = '8px sans-serif';
ctx.strokeStyle = 'black';
// Draw HRRR color ramp and labels
let labelNum = 0;
zeroLen_HRRR_ramp = HRRR_ramp.length - 1;
let gradient = ctx.createLinearGradient(0, 0, rampWidth, 0);
for (let i = 0; i < HRRR_ramp.length; i++) {
let rampStop = HRRR_ramp[i];
let stop = i / zeroLen_HRRR_ramp;
gradient.addColorStop(stop, rampStop["color"]);
if (i == 0) {
// First label and tic
let x = leftMargin + (stop * rampWidth);
ctx.fillText(rampStop["label"], x - firstLabelXoffset, labelYstart);
// Draw tic
ctx.beginPath();
ctx.moveTo(x + endTicXoffset, rampHeight);
ctx.lineTo(x + endTicXoffset, ticYstop);
ctx.stroke();
} else if (i % 32 == 0) {
// Intermediate labels and tic
let x = leftMargin + (stop * rampWidth);
ctx.fillText(rampStop["label"], x - labelXoffset, labelYstart);
// Draw tic
ctx.beginPath();
ctx.moveTo(x, rampHeight);
ctx.lineTo(x, ticYstop);
ctx.stroke();
} else if (i == 255) {
// Final label and tic
let x = leftMargin + (stop * rampWidth);
ctx.fillText(rampStop["label"] + " dBZ", x - labelXoffset, labelYstart);
// Draw tic
ctx.beginPath();
ctx.moveTo(x - endTicXoffset, rampHeight);
ctx.lineTo(x - endTicXoffset, ticYstop);
ctx.stroke();
}
}
ctx.fillStyle = gradient;
ctx.fillRect(leftMargin, topMargin, rampWidth, rampHeight);
</script>
</body>
</html>
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