R: Empirical Intensity of Point Pattern

intensity.ppp {spatstat.geom} | R Documentation

## 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 Adrian.Baddeley@curtin.edu.au

and Rolf Turner r.turner@auckland.ac.nz

### 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))

[Package spatstat.geom version 2.3-2 Index]