[R-sig-Geo] [FORGED] spatstat residuals.ppm with an intensity given as an image?

[Rolf Turner]

On 07/06/17 22:22, Seth Flaxman wrote:

> I've got the intensity of an inhomogeneous Poisson process (fit using
> some new methods I'm working on, so not created by spatstat) as an
> image object, the observed point pattern as a ppp object, and I'd like
> to call residuals.ppm to compute residuals. Is there a simple way to
> create a fitted point process model (ppm) from an image and points so
> I can pass this directly to residuals.ppm?

Sorry for the long delay in responding.

There are two ways to do this:

[1] Fit a model using the putative intensity as an offset:

              fit1 <- ppm(X ~ offset(log(lam)))

where 'lam' is the pixel image of intensity, and 'X' is the point pattern.

Then do:

            res <- residuals(fit1)

[2] Fit some other model (e.g. just a constant intensity model) and use 
the argument 'fittedvalues' of residuals.ppm to specify the fitted 
intensity values.

            fit2 <- ppm(X ~ 1, forcefit=TRUE)

            res  <- residuals(fit2, fittedvalues=lam[quad.ppm(fit2)])

cheers,

Rolf Turner

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