Given an rgb value, return date, confidence, and intensity for GLAD alerts

decode_date.js

        var decode_date = function(rgba) {

            // find the total days of the pixel by
            // multiplying the red band by 255 and adding
            // the green band to that
            var total_days = rgba[0] * 255 + rgba[1];

            // take the total days value and divide by 365 to
            // get the year_offset. Add 15 to this (i.e 0 + 15 = 2015)
            // or 1 + 15 = 2016
            var year_int = parseInt(total_days / 365) + 15;

            // Multiply by 1000 to give us year in YYDDD format
            // (i.e. 15000 or 16000)
            var year = parseInt((year_int * 1000))

            // Find the remaining days to get the julian day for
            // that year
            var julian_day = total_days % 365;

            // Add to get YYDDD date val
            var date_val = year + julian_day;

            // Convert the blue band to string, leading
            // zeros if it's not currently three digits
            // this occurs very rarely; where there's an intensity
            // value but no date/confidence for it. Due to bilinear
            // resampling
            var band3_str = pad(rgba[2].toString());

            // Grab confidence (the first value) from this string
            // confidence is stored as 1/2, subtract one to make it 0/1
            var confidence = parseInt(band3_str[0]) - 1

            // Grab the raw intensity value from the pixel; ranges from 1 - 55
            var intensity_raw = parseInt(band3_str.slice(1, 3))

            // Scale the intensity to make it visible
            var intensity = intensity_raw * 50

            // Set intensity to 255 if it's > than that value
            if (intensity > 255) {
                intensity = 255
            }

            return [date_val, confidence, intensity]

        };