# distmap.ppp

##### Distance Map of Point Pattern

Computes the distance from each pixel to the nearest point in the given point pattern.

##### Usage

```
# S3 method for ppp
distmap(X, …)
```

##### Arguments

- X
A point pattern (object of class

`"ppp"`

).- …
Arguments passed to

`as.mask`

to control pixel resolution.

##### Details

The ``distance map'' of a point pattern \(X\) is the function
\(f\) whose value `f(u)`

is defined for any two-dimensional
location \(u\) as the shortest distance from \(u\) to \(X\).

This function computes the distance map of the point pattern `X`

and returns the distance map as a pixel image. The greyscale value
at a pixel \(u\) equals the distance from \(u\) to the nearest
point of the pattern `X`

.

Additionally, the return value
has two attributes, `"index"`

and `"bdry"`

, which are
also pixel images. The grey values in `"bdry"`

give the
distance from each pixel to the bounding rectangle of the image.
The grey values in `"index"`

are integers identifying which
point of `X`

is closest.

This is a method for the generic function `distmap`

.

Note that this function gives the distance from the
*centre of each pixel* to the nearest data point.
To compute the exact distance from a given spatial location
to the nearest data point in `X`

, use `distfun`

or
`nncross`

.

##### Value

A pixel image (object of class `"im"`

) whose greyscale values
are the values of the distance map.
The return value has attributes `"index"`

and `"bdry"`

which are also pixel images.

##### See Also

Generic function `distmap`

and other methods
`distmap.psp`

,
`distmap.owin`

.

Generic function `distfun`

.

Nearest neighbour distance `nncross`

##### Examples

```
# NOT RUN {
data(cells)
U <- distmap(cells)
# }
# NOT RUN {
plot(U)
plot(attr(U, "bdry"))
plot(attr(U, "index"))
# }
```

*Documentation reproduced from package spatstat, version 1.55-1, License: GPL (>= 2)*