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convert.js
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convert.js
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// http://srtm.csi.cgiar.org/download
// Usage: convert.js srtm_1.asc ...
const fs = require("fs");
const files = process.argv.slice(2);
files.forEach(file => {
console.log(`Processing ${file}`);
const out = convert(file);
const filename = `strm3_${out.y}_${out.x}.strmb`;
console.log(`Writting ${filename}`);
fs.writeFileSync(filename, out.elevations);
});
function convert(filename) {
const lines = fs.readFileSync(filename, {encoding: 'utf8'}).split("\n");
const elevations = [];
if (lines.length < 6000 + 6) {
throw new Error(`Invalid file`);
}
let x;
let y;
// Process the header
for (let i = 0; i < 6; i++) {
let parts = lines.shift().split(/\s+/);
if (parts.length >= 2) {
switch (parts[0].toLowerCase()) {
case "xllcorner":
x = Math.round(parts[1]);
break;
case "yllcorner":
y = Math.round(parts[1]);
break;
}
}
}
if (x == null || y == null) {
throw new Error(`Invalid file`);
}
// Process the elevation data
for (let i = 0; i < 6000; i++) {
let parts = lines.shift().split(/\s+/);
if (parts.length < 6000) {
throw new Error(`Invalid file`);
}
for (let j = 0; j < 6000; j++) {
let elevation = Number(parts[j]);
if (elevation < 0) {
elevation = 0;
}
elevation = Math.round(1 + (elevation + 10) / 20);
elevations.push(elevation);
}
}
return {
x: x,
y: y,
elevations: Uint8Array.from(elevations)
};
}