R: Kernel Estimate of Intensity as a Spatial Function

densityfun.ppp {spatstat.core} | R Documentation

## Kernel Estimate of Intensity as a Spatial Function

### Description

Compute a kernel estimate of intensity for a point pattern, and return the result as a function of spatial location.

### Usage

    densityfun(X, ...)

    ## S3 method for class 'ppp'
    densityfun(X, sigma = NULL, ...,
                            weights = NULL, edge = TRUE, diggle = FALSE)

### Arguments

`X` | Point pattern (object of class `"ppp"`).
`sigma` | Smoothing bandwidth, or bandwidth selection function, passed to `density.ppp`.
`...` | Additional arguments passed to `density.ppp`.
`weights` | Optional vector of weights associated with the points of `X`.
`edge,diggle` | Logical arguments controlling the edge correction. Arguments passed to `density.ppp`.

### Details

The commands `densityfun` and `density` both perform kernel estimation of the intensity of a point pattern. The difference is that `density` returns a pixel image, containing the estimated intensity values at a grid of locations, while `densityfun` returns a `function(x,y)` which can be used to compute the intensity estimate at any spatial locations with coordinates `x,y`. For purposes such as model-fitting it is more accurate to use `densityfun`.

### Value

A `function` with arguments `x,y,drop`. The function also belongs to the class `"densityfun"` which has methods for `print` and `as.im`. It also belongs to the class `"funxy"` which has methods for `plot`, `contour` and `persp`.

### Using the result of `densityfun`

If `f <- densityfun(X)`, where `X` is a two-dimensional point pattern, the resulting object `f` is a `function` in the R language.

By calling this function, the user can evaluate the estimated intensity at any desired spatial locations.

Additionally `f` belongs to other classes which allow it to be printed and plotted easily.

The function `f` has arguments `x,y,drop`.

- The arguments `x,y` of `f` specify the query locations. They can be numeric vectors of coordinates. Alternatively `x` can be a point pattern (or data acceptable to `as.ppp`) and `y` is omitted. The result of `f(x,y)` is a numeric vector giving the values of the intensity.

- The argument `drop` of `f` specifies how to handle query locations which are outside the window of the original data. If `drop=TRUE` (the default), such locations are ignored. If `drop=FALSE`, a value of `NA` is returned for each such location.

Note that the smoothing parameters, such as the bandwidth `sigma`, are assigned when `densityfun` is executed. Smoothing parameters are fixed inside the function `f` and cannot be changed by arguments of `f`.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner r.turner@auckland.ac.nz and Ege Rubak rubak@math.aau.dk.

### See Also

`density`.

To interpolate values observed at the points, use `Smoothfun`.

### Examples

      f <- densityfun(swedishpines)
      f
      f(42, 60)
      X <- runifpoint(2, Window(swedishpines))
      f(X)
      plot(f)

[Package spatstat.core version 2.3-0 Index]