SDMTools (version 1.1-221)

COGravity: Centre of Gravity or Mass calculations for spatial data

Description

COGravity calculates the Centre of Gravity (or also known as Centre of Mass) for point or raster spatial data. Note: NA data is automatically ommitted from analysis.

Usage

COGravity(x, y = NULL, z = NULL, wt = NULL)

Arguments

x

a vector of e.g., longitudes or eastings, or a raster of class 'asc', 'RasterLayer' or 'SpatialGridDataFrame'.

y

a vector of e.g., latitudes or northings.

z

a vector of e.g., elevations.

wt

a vector or raster of class 'asc', 'RasterLayer' or 'SpatialGridDataFrame' representing weights for data.

Value

Returns a named vector of data representing the Centre of Gravity in x, y & z dimensions (depending on data supplied).

Details

For raster-based data, if wt is missing, the values of the ascii are assumed to be the weights; otherwise, the values are assumed to be the z values.

Examples

#create some points
x = seq(154,110,length=25)
y = seq(-10,-54,length=25)
z = seq(100,200,length=25)
wt = runif(25) #random weights
#calculate the Centre of Gravity for these points
COGravity(x,y,z,wt)

#create a simple objects of class 'asc'
x = as.asc(matrix(1:50,nr=50,nc=50))
wt = as.asc(matrix(runif(50),nr=50,nc=50))

#calculate COG with weighting defined in x
COGravity(x)
#calculate COG with weighting defined in wt (values in x are assumed elevation (z))
COGravity(x,wt=wt)