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.
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.