distance {sphet}

Distance measures available in distance

Description

Reads points coordinates and generates objects of class distance.matrix

Usage

distance(coord, region.id = NULL, output = TRUE,
type = c("NN", "distance", "inverse"),
measure = c("euclidean", "gcircle", "chebyshev", "braycur", "canberra"),
nn = 6, cutoff = FALSE, miles = TRUE, R = NULL, shape.name = NULL, region.id.name = NULL,
firstline = FALSE, file.name = NULL)

Arguments

coord

a matrix with the (X,Y)-coordinates of the points. The first column can be the region.id variable giving the ordering of the observations

region.id

variable that defines the ordering of the observations

output

when TRUE (default) writes the object to a file

type

one of ("NN","distance","inverse"). Nearest neighbors, distance or inverse distance

measure

one of ("euclidean","gcircle","chebyshev","braycur","canberra").The distance measure to be employed in the calculations (See Details)

nn

the number of nearest neighbors

cutoff

If type is distance or inverse. Assumes values 1, 2 or 3. When 1, the cutoff is set to the first quantile of the distribution of distances. When 2 to the median, and when 3 to the third quantile. Only observations with distance less than cutoff distance are neighbors.

miles

If TRUE (default), distances are in miles, otherwise in Km. (See spDists wcich returns km, and are converted if required)

R

deprecated, spDists uses an approximation to the WGS84 spheroid

shape.name

The name of the shape file. See Details

region.id.name

The name of the region.id variable. See Details

firstline

If TRUE, a first line is added to the output file. See Details

file.name

If output, the name of the output file. See Details

Details

Writes distance matrices

The object created is similar to the content of a 'GWT' file. The output file can be of any format. In particular, it could be a 'GWT' file. When firstline is TRUE, an header line is added to the 'GWT' file. The first element is simply a place holder, the second is the number of observations. The name of the shape file and of the id variable can be specified by the options shape.name and region.id.name respectively. The function performs a series of test on the region.id variable. If a region.id variable is not specified and coord only has two columns, a sequence from 1 to the number of observations is generated and used as identification variable. If region.id is specified and the first column of coord contains an id variable they should be the same.

The distance measures implemented in sphet are:

• 'euclidean': \sqrt{\sum{(x_i - y_i)^2}}

• 'chebyshev': max(|x_i - y_i|)

• 'braycur': \frac{\sum{|x_i - y_i|}}{\sum{|x_i + y_i|}}

• 'canberra': \frac{\sum{|x_i - y_i|}}{\sum{|x_i| + |y_i|}}

• 'gcircle': see spDists, which uses an approximation to the WGS84 spheroid.

Value

A matrix of three columns: from, to, and distance

Author(s)

Gianfranco Piras [e-mail]

Examples

 
set.seed("1234")
X <- runif(100, 0, 70)
Y <- runif(100, -30, 20)
coord1 <- cbind(seq(1,100), X, Y)
thm2 <- distance(coord1, region.id = NULL, 
output = FALSE, type = "NN", nn = 6)
thm2 <- distance(coord1, region.id = NULL, output = FALSE, type = "distance", cutoff = 1)