Hi everyone,

According to SNAP’s help PVI has **PVI = sin(a) * IR_factor * near_IR - cos(a) * red_factor * red** formula.

According to https://www.asprs.org/wp-content/uploads/pers/1977journal/dec/1977_dec_1541-1552.pdf (the original article where this index was proposed) it has **PVI = sqrt((Rgg5-Rp5)2 + (Rgg7-Rp7)^2),** formula,

or according to http://www.mdpi.com/2072-4292/4/12/3892/htm#b31-remotesensing-04-03892

it has (pNIR –α pred – b)/(1+α2)

pNIR,soil = α pred,soil+b formula.

There is no sin or cos in initial formula? Why does SNAP use its own formula?