R/ARmodis.R

In klauswiese/AngleIndexes: AngleIndexes

#Función AR para MODIS
ARmodis <- function(Green, Red, NIR){
  ARIndex <- overlay(Green, Red, NIR, fun=function(x,y,z){
    a <- (sqrt((0.648-0.555)^2+(y-x)^2))
    b <- (sqrt((0.858-0.648)^2+(z-y)^2))
    c <- (sqrt((0.858-0.555)^2+(z-x)^2))
    d <- (a^2+b^2-c^2)/(2*a*b)
    d2 <- ifelse(d > 1, 1, ifelse(d < -1, -1, d))
    ind <- acos(d2)
    return(ind)
  })
  return(ARIndex)
}