id_64.js

//
// Perpendicular Vegetation Index  (abbrv. PVI)
//
// General formula: (1 / sqrt(a^2+ 1)) * (NIR - ar - b)
//
// URL https://www.indexdatabase.de/db/si-single.php?sensor_id=96&rsindex_id=64
//

// Initialize parameters
let a = 0.149;
let ar = 0.374;
let b = 0.735;

let index = (1.0 / Math.sqrt(Math.pow(a, 2.0) + 1.0)) * (B08 - ar - b);
let min = -1.58;
let max = 0.101;
let zero = 0.0;

// colorBlend will return a color when the index is between min and max and white when it is less than min.
// To see black when it is more than max, uncomment the last line of colorBlend.
// The min/max values were computed automatically and may be poorly specified, feel free to change them to tweak the displayed range.
// This index crosses zero, so a diverging color map is used. To tweak the value of the break in the color map, change the variable 'zero'.

let underflow_color = [1, 1, 1];
let low_color = [208/255, 88/255, 126/255];
let high_color = [241/255, 234/255, 200/255];
let zero_color = [0, 147/255, 146/255];
let overflow_color = [0, 0, 0];

return colorBlend(index, [min, min, zero, max],
[
	underflow_color,
	low_color,
	zero_color, // divergent step at zero
	high_color,
	//overflow_color // uncomment to see overflows
]);