densityfun.ppp | R Documentation |

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

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

`X` |
Point pattern (object of class |

`sigma` |
Smoothing bandwidth, or bandwidth selection function,
passed to |

`...` |
Additional arguments passed to |

`weights` |
Optional vector of weights associated with the points of |

`edge` , `diggle` |
Logical arguments controlling the edge correction.
Arguments passed to |

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`

.

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`

.

`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`

.

.

`density`

.

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

.

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

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