intensity.ppp {spatstat.geom}

Empirical Intensity of Point Pattern

Description

Computes the average number of points per unit area in a point pattern dataset.

Usage

## S3 method for class 'ppp'
intensity(X, ..., weights=NULL)

## S3 method for class 'splitppp'
intensity(X, ..., weights=NULL)

Arguments

X

A point pattern (object of class "ppp").

weights

Optional. Numeric vector of weights attached to the points of X. Alternatively, an expression which can be evaluated to give a vector of weights.

...

Ignored.

Details

This is a method for the generic function intensity. It computes the empirical intensity of a point pattern (object of class "ppp"), i.e. the average density of points per unit area.

If the point pattern is multitype, the intensities of the different types are computed separately.

Note that the intensity will be computed as the number of points per square unit, based on the unit of length for X, given by unitname(X). If the unit of length is a strange multiple of a standard unit, like 5.7 metres, then it can be converted to the standard unit using rescale. See the Examples.

If weights are given, then the intensity is computed as the total weight per square unit. The argument weights should be a numeric vector of weights for each point of X (weights may be negative or zero).

Alternatively weights can be an expression which will be evaluated for the dataset to yield a vector of weights. The expression may involve the Cartesian coordinates x,y of the points, and the marks of the points, if any. Variable names permitted in the expression include x and y, the name marks if X has a single column of marks, the names of any columns of marks if X has a data frame of marks, and the names of constants or functions that exist in the global environment. See the Examples.

Value

A numeric value (giving the intensity) or numeric vector (giving the intensity for each possible type).

Author(s)

Adrian Baddeley [e-mail]

and Rolf Turner [e-mail]

See Also

intensity, intensity.ppm

Examples

  japanesepines
  intensity(japanesepines)
  unitname(japanesepines)
  intensity(rescale(japanesepines))

  intensity(amacrine)
  intensity(split(amacrine))

  # numeric vector of weights
  volumes <- with(marks(finpines), (pi/4) * height * diameter^2)
  intensity(finpines, weights=volumes)

  # expression for weights
  intensity(finpines, weights=expression((pi/4) * height * diameter^2))