approxNA {raster} | R Documentation

## Estimate values for cell values that are `NA` by interpolating between layers

### Description

approxNA uses the `stats` function `approx` to estimate values for cells that are `NA` by interpolation across layers. Layers are considered equidistant, unless an argument 'z' is used, or `getZ` returns values, in which case these values are used to determine distance between layers.

For estimation based on neighbouring cells see `focal`

### Usage

    ## S4 method for signature 'RasterStackBrick'
    approxNA(x, filename="", method="linear", yleft, yright,
                rule=1, f=0, ties=mean, z=NULL, NArule=1, ...)

### Arguments

`x` | RasterStack or RasterBrick object
`filename` | character. Output filename (optional)
`method` | specifies the interpolation method to be used. Choices are "linear" or "constant" (step function; see the example in `approx`
`yleft` | the value to be returned before a non-`NA` value is encountered. The default is defined by the value of rule given below
`yright` | the value to be returned after the last non-`NA` value is encountered. The default is defined by the value of rule given below
`rule` | an integer (of length 1 or 2) describing how interpolation is to take place at for the first and last cells (before or after any non-`NA` values are encountered). If rule is 1 then NAs are returned for such points and if it is 2, the value at the closest data extreme is used. Use, e.g., `rule = 2:1`, if the left and right side extrapolation should differ
`f` | for method = "constant" a number between 0 and 1 inclusive, indicating a compromise between left- and right-continuous step functions. If y0 and y1 are the values to the left and right of the point then the value is `y0*(1-f)+y1*f` so that `f = 0)` is right-continuous and `f = 1` is left-continuous
`ties` | Handling of tied 'z' values. Either a function with a single vector argument returning a single number result or the string "ordered"
`z` | numeric vector to indicate the distance between layers (e.g., time, depth). The default is 1:nlayers(x)
`NArule` | single integer used to determine what to do when only a single layer with a non-`NA` value is encountered (and linear interpolation is not possible). The default value of 1 indicates that all layers will get this value for that cell; all other values do not change the cell values
`...` | additional arguments as for `writeRaster`

### Value

RasterBrick

### See Also

`focal`

### Examples

    r <- raster(ncols=5, nrows=5)
    r1 <- setValues(r, runif(ncell(r)))
    r2 <- setValues(r, runif(ncell(r)))
    r3 <- setValues(r, runif(ncell(r)))
    r4 <- setValues(r, runif(ncell(r)))
    r5 <- setValues(r, NA)
    r6 <- setValues(r, runif(ncell(r)))
    r1[6:10] <- NA
    r2[5:15] <- NA
    r3[8:25] <- NA
    s <- stack(r1,r2,r3,r4,r5,r6)
    s[1:5] <- NA
    x1 <- approxNA(s)
    x2 <- approxNA(s, rule=2)
    x3 <- approxNA(s, rule=2, z=c(1,2,3,5,14,15))

[Package raster version 2.5-2 Index]