Learn R Programming
GeoModels (version 2.2.1)

GeoOutlier: Spatio (temporal) outliers detection

Description

Given a set of spatio (temporal) locations and data, the procedure select the spatial or spatiotemporal ouliers using a specific algorithm.

Usage

GeoOutlier(data, coordx, coordy=NULL,coordz=NULL, coordt=NULL, coordx_dyn=NULL, 
             distance="Eucl", grid=FALSE,  neighb=10,alpha=0.001,
             method="Z-Median", radius=1, bivariate=FALSE,X=NULL)

Value

Return a matrix or a list containing the dected spatial or spatio-temporal outliers

Arguments

data

An optional \(d\)-dimensional vector (a single spatial realisation) or a (\(d \times d\))-matrix (a single spatial realisation on regular grid) or a (\(t \times d\))-matrix (a single spatial-temporal realisation) or an (\(d \times d \times t \times n \))-array (a single spatial-temporal realisation on regular grid).

coordx

A numeric (\(d \times 2\))-matrix or (\(d \times 3\))-matrix Coordinates on a sphere for a fixed radius radius are passed in lon/lat format expressed in decimal degrees.

coordy

A numeric vector giving 1-dimension of spatial coordinates; Optional argument, the default is NULL.

coordz

A numeric vector giving 1-dimension of spatial coordinates; Optional argument, the default is NULL.

coordt

A numeric vector giving 1-dimension of temporal coordinates. Optional argument, the default is NULL then a spatial RF is expected.

coordx_dyn

A list of \(m\) numeric (\(d_t \times 2\))-matrices containing dynamical (in time) spatial coordinates. Optional argument, the default is NULL

distance

String; the name of the spatial distance. The default is Eucl, the euclidean distance. See the Section Details of GeoFit.

grid

Logical; if FALSE (the default) the data are interpreted as spatial or spatial-temporal realisations on a set of non-equispaced spatial sites (irregular grid).

neighb

Numeric; an optional positive integer indicating the order of neighborhoodused for Z-Median algorithm.

alpha

Numeric; a numeric value between 0 and 1 used for Z-Median algorithm.

method

String; The name of the algorithm for detecting spatial ouliers. Default is Z-median proposed in Chen et al. (2008)

radius

Numeric; a value indicating the radius of the sphere when using the great circle distance. Default value is 1.

bivariate

If TRUE then data is considered as spatial bivariate data.

X

Numeric; an optional Matrix of spatio (temporal) covariates.

References

Chen D, Lu C, Kou Y, Chen F (2008) On detecting spatial outliers. Geoinformatica 12:455–475

Bevilacqua M., Caamaño C., Arellano-Valle R. B., Camilo Gomez C. (2022) A class of random fields with two-piece marginal distributions for modeling point-referenced data with spatial outliers. Test 10.1007/s11749-021-00797-5

Examples

Run this code

library(GeoModels)
set.seed(1428)
NN = 1500
coords = cbind(runif(NN),runif(NN))
###
scale=0.5/3
corrmodel = "Matern"; 

param = list(mean=0,sill=1,nugget=0,scale=scale,smooth=0.5,skew=0)
data = GeoSim(coordx = coords,corrmodel = corrmodel,
                  model = "TwoPieceGaussian",param = param)$data

K=15         #parameter for outliers detection alghoritm
alpha=0.005  #parameter for outliers detection alghoritm
outlier=GeoOutlier(data=data, coordx = coords,neighb=K,alpha=alpha)
quilt.plot(coords,data)
for (i in 1:nrow(outlier))  plotrix::draw.circle(outlier[i,1], outlier[i,2],radius=0.02,lwd=2) 
nrow(outlier) # number of outliers

param = list(mean=0,sill=1,nugget=0.4,scale=scale,smooth=0.5)
data = GeoSim(coordx = coords,corrmodel = corrmodel,
                  model = "Gaussian",param = param)$data

K=15         #parameter for outliers detection alghoritm
alpha=0.005  #parameter for outliers detection alghoritm
outlier=GeoOutlier(data=data, coordx = coords,neighb=K,alpha=alpha)
quilt.plot(coords,data)
for (i in 1:nrow(outlier))  plotrix::draw.circle(outlier[i,1], outlier[i,2],radius=0.02,lwd=2)
nrow(outlier) # number of outliers

Run the code above in your browser using DataLab