spatstat (version 1.6-4)

update.ppm: Update a Fitted Point Process Model

Description

update method for class "ppm".

Usage

update.ppm(object, ...,
            Q, trend, interaction, covariates,
            correction, rbord, use.gam, forcefit)

Arguments

object

An existing fitted point process model, typically produced by ppm.

...

Unnamed arguments - see Details.

Q

a new point pattern dataset or quadrature scheme to which the model should be fitted. An object of class "ppp" or "quad".

trend

a new formula for the spatial trend of the model.

interaction

a new interpoint interaction structure (object of class "interact") for the model.

covariates

a new data frame of spatial covariates, or NULL to remove all spatial covariates.

correction

character string giving a new type of edge correction, or NULL to return to the default.

rbord

numerical value of the distance for the `border' edge correction, or NULL to suppress the border correction.

use.gam

logical value indicating whether to fit the model using gam. See ppm.

forcefit

logical value controlling the use of shortcuts when fitting trivial models. See ppm.

Value

• Another fitted point process model (object of class "ppm").

Details

This is a method for the generic function update for the class "ppm". An object of class "ppm" describes a fitted point process model. See ppm.object) for details of this class.

update.ppm will modify the point process model specified by object according to the new arguments given, then re-fit it. The actual re-fitting is performed by the model-fitting function ppm.

If you are comparing several model fits to the same data, or fits of the same model to different data, it is strongly advisable to use update.ppm rather than trying to fit them by hand. This is because update.ppm re-fits the model in a way which is comparable to the original fit.

The named arguments Q, trend, interaction, covariates, correction, rbord, use.gam and forcefit are passed to ppm. Use name=NULL to remove the argument name from the call.

The unnamed arguments ... may include

• exactly one argument of class"ppp"or"quad", which will be interpreted as the named argumentQ;
• exactly one argument of class"formula", which will be interpreted as the named argumenttrend;
• exactly one argument of class"interact", which will be interpreted as the named argumentinteraction;
• exactly one argument of class"data.frame", which will be interpreted as the named argumentcovariates.

Examples

data(nztrees)
  data(cells)

  # fit the stationary Poisson process
  fit <- ppm(nztrees, ~ 1)

  # fit a nonstationary Poisson process
  fitP <- update(fit, trend=~x)
  fitP <- update(fit, ~x)

  # fit a stationary Strauss process
  fitS <- update(fit, interaction=Strauss(13))
  fitS <- update(fit, Strauss(13))

  # oops, forgot the edge correction
  fitS <- update(fitS, rbord=13)

  # re-fit the model to a subset
  # of the original point pattern
  nzw <- owin(c(0,148),c(0,95))
  nzsub <- nztrees[,nzw]
  fut <- update(fitS, Q=nzsub)
  fut <- update(fitS, nzsub)

  # WARNING: the point pattern argument is called 'Q'

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