This is a method for the generic function intensity
for fitted point process models (class "ppm"). The intensity of a point process model is the expected
number of random points per unit area.
If X is a Poisson point process model, the intensity of the
process is computed exactly.
The result is a numerical value if X
is a stationary Poisson point process, and a pixel image if X
is non-stationary. (In the latter case, the resolution of the pixel
image is controlled by the arguments ... which are passed
to predict.ppm.)
If X is another Gibbs point process model, the intensity is
computed approximately using the Poisson-saddlepoint approximation
(Baddeley and Nair, 2012a, 2012b, 2016; Anderssen et al, 2014).
The approximation is currently available for pairwise-interaction
models (Baddeley and Nair, 2012a, 2012b)
and for the area-interaction model and Geyer saturation model
(Baddeley and Nair, 2016).
For a non-stationary Gibbs model, the
pseudostationary solution (Baddeley and Nair, 2012b;
Anderssen et al, 2014) is used. The result is a pixel image,
whose resolution is controlled by the arguments ... which are passed
to predict.ppm.