Gap filling temporal raster objects

Question

Suppose I have 4 raster layers each belong to every other week of the month. I want to use linear interpolation to create new layers for each day. In this case, the first 2 rast

Answer 1

About the same question was asked two weeks ago. Here is the adapted answer for your example.

library(raster)
r1 <- raster(nrow=5, ncol=5)
feb15 <- setValues(r1, runif(ncell(r1)))
feb29 <- setValues(r1, runif(ncell(r1)))
mar15 <- setValues(r1, runif(ncell(r1)))
mar30 <- setValues(r1, runif(ncell(r1)))

s <- stack(feb15, feb29, mar15, mar30)
x <- calc(s, fun=function(y) approx(c(15,29,29+15,29+30), y, 1:59, rule=2)$y)
names(x) <- c(paste('feb', 1:29), paste('march', 1:30))

Unfortunately, approx fails when it only gets NA values. It "need at least two non-NA values to interpolate". Here is a work around:

s[1:2] <- NA
# fail <- calc(s, fun=function(y) approx(c(15,29,29+15,29+30), y, 1:59, rule=2)$y)

f <- function(y) {
    if (sum(! is.na(y)) < 2) {
        return(rep(NA, 59))
    } else {
        approx(c(15,29,29+15,29+30), y, 1:59, rule=2)$y
    }
}

x <- calc(s, fun=f)