Calculating pressure reduced to sea level (JavaScript)

Problem

The pressure as it is read from the BMP180 sensor is an absolute pressure. To be able to compare it with other sensors it is necessary to have a common level above the sea. For example the value of pressure as it is given in your weather forecast is reduced to the sea level. How do we do that in JavaScript?

The solution

The following calculateSeaLevelPressure() function is based on this blog post (in polish!) and validated using a PHP implementation

	function calculateSeaLevelPressure(p, t, h) {
	h = h || 240;
	p = p / 100.0;
	hp = 8000 * ((1 + 0.004 * t) / p);
	px = p + (h/hp);
	pd = (px + p) / 2;
	tp = t + ((0.6 * h) / 100);
	td = (t + tp) / 2;
	hp = 8000 * ((1 + 0.004 * td) / pd);
	pn = p + (h / hp);
	return pn;
	}

view raw pressure-calc.js hosted with ❤ by GitHub

Happy coding!