# approximate: Estimate values for cell values that are 'NA' by... In terra: Spatial Data Analysis

 approximate R Documentation

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

### Description

approximate uses the `stats` function `approx` to estimate values for cells that are `NA` by interpolation across layers. Layers are considered equidistant, unless argument `z` is used, or `time(x)` returns values that are not `NA`, in which case these values are used to determine distance between layers.

For estimation based on neighboring cells see `focal`

### Usage

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

### Arguments

 `x` SpatRaster `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., depth). The default is `time(x)` if these are not `NA` or else `1:nlys(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 `filename` character. Output filename `...` additional arguments for writing files as in `writeRaster`

### Value

SpatRaster

` focal`, `fillTime`

### Examples

``````r <- rast(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 <- c(r1,r2,r3,r4,r5,r6)
s[1:5] <- NA
x1 <- approximate(s)
x2 <- approximate(s, rule=2)
x3 <- approximate(s, rule=2, z=c(1,2,3,5,14,15))

``````

terra documentation built on Oct. 13, 2023, 5:08 p.m.