# layerCor: Correlation and (weighted) covariance In terra: Spatial Data Analysis

 layerCor R Documentation

## Correlation and (weighted) covariance

### Description

Compute correlation, (weighted) covariance, or similar summary statistics that compare the values of all pairs of the layers of a SpatRaster.

### Usage

``````## S4 method for signature 'SpatRaster'
layerCor(x, fun, w, asSample=TRUE, na.rm=FALSE, maxcell=Inf, ...)
``````

### Arguments

 `x` SpatRaster `fun` character. The statistic to compute: either "cov" (covariance), "weighted.cov" (weighted covariance), or "pearson" (correlation coefficient) or your own function that takes two vectors as argument to compute a single number `w` SpatRaster with the weights to compute the weighted covariance. It should have a single layer and the same geometry as `x` `asSample` logical. If `TRUE`, the statistic for a sample (denominator is `n-1`) is computed, rather than for the population (denominator is `n`). Only for the standard functions `na.rm` logical. Should missing values be removed? `maxcell` postive integer. The number of cells to be regularly sampled. Only used when `fun` is a function `...` additional arguments for `fun` (if it is a proper function)

### Value

If `fun` is one of the three standard statistics, you get a list with two items: the correlation or (weighted) covariance matrix, and the (weighted) means.

If `fun` is a function, you get a matrix.

### References

For the weighted covariance:

• Canty, M.J. and A.A. Nielsen, 2008. Automatic radiometric normalization of multitemporal satellite imagery with the iteratively re-weighted MAD transformation. Remote Sensing of Environment 112:1025-1036.

• Nielsen, A.A., 2007. The regularized iteratively reweighted MAD method for change detection in multi- and hyperspectral data. IEEE Transactions on Image Processing 16(2):463-478.

`global`, `cov.wt`, `weighted.mean`

### Examples

``````b <- rast(system.file("ex/logo.tif", package="terra"))
layerCor(b, "pearson")

layerCor(b, "cov")

# weigh by column number
w <- init(b, fun="col")
layerCor(b, "weighted.cov", w=w)
``````

terra documentation built on April 22, 2023, 1:16 a.m.