RStoolbox (version 0.1.6)

rasterCVA: Change Vector Analysis

Description

Calculates angle and magnitude of change vectors. Dimensionality is limited to two bands per image.

Usage

rasterCVA(x, y, tmf = 2, ...)

Arguments

x

RasterBrick or RasterStack with two layers. This will be the reference/origin for the change calculations. Both rasters (y and y) need to correspond to each other, i.e. same resolution, extent and origin.

y

RasterBrick or RasterStack with two layers. Both rasters (y and y) need to correspond to each other, i.e. same resolution, extent and origin.

tmf

Numeric. Threshold median factor. Used to calculate a threshold magnitude for which pixels are considered stable, i.e. no change. Defaults to 2 times the median non-zero magnitude. Calculated as tmf * median(magnitude[magnitude > 0])

...

further arguments passed to writeRaster

Value

Returns a RasterBrick with two layers: change vector angle and change vector magnitude

Details

Change Vector Analysis (CVA) is used to identify spectral changes between two identical scenes which were acquired at different times. CVA is limited to two bands per image. For each pixel it calculates the change vector in the two-dimensional spectral space. For example for a given pixel in image A and B for the red and nir band the change vector is caclulated for the coordinate pairs: (red_A | nir_A) and (red_B | nir_B).

The coordinate system is defined by the order of the input bands: the first band defines the x-axis and the second band the y-axis, respectively. Angles are returned *in degree* beginning with 0 degrees pointing 'north', i.e. the y-axis, i.e. the second band.

Examples

library(raster)
## Create example data
data(lsat)
pca <- rasterPCA(lsat)$map

## Do change vector analysis 
cva <- rasterCVA(pca[[1:2]], pca[[3:4]])
cva
plot(cva)