spatstat.geom (version 3.2-9)

distmap.psp: Distance Map of Line Segment Pattern

Description

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

Usage

# S3 method for psp
distmap(X, ..., extras=TRUE, clip=FALSE, metric=NULL)

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.

Arguments

X

A line segment pattern (object of class "psp").

...

Arguments passed to as.mask to control pixel resolution.

extras

Logical value specifying whether to compute the additional attributes "index" and "bdry" described in Details.

clip

Logical value specifying whether the resulting pixel image should be clipped to the window of X.

metric

Optional. A distance metric (object of class "metric", see metric.object) which will be used to compute the distances.

Author

Adrian Baddeley , Rolf Turner and Ege Rubak .

Details

The ``distance map'' of a line segment 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 line segment 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 line segment of the pattern X. Distances are computed using analytic geometry.

The result is a pixel image. If clip=FALSE (the default), the pixel values are defined at every pixel in the rectangle Frame(X). If clip=TRUE, the pixel values are defined only inside Window(X), and are NA outside this window. Computation is faster when clip=FALSE.

Additionally, if extras=TRUE, the return value has two attributes, "index" and "bdry", which are also pixel images. The pixels values of "bdry" give the distance from each pixel to the boundary of the window of X (and are zero outside this window). The pixel values of "index" are integers identifying which line segment of X is closest. If clip=FALSE (the default), these images are defined at every pixel in Frame(X); if clip=TRUE, they are clipped to the window of X. Computation is faster when extras=FALSE.

This is a method for the generic function distmap.

Note that this function gives the exact distance from the centre of each pixel to the nearest line segment. To compute the exact distance from the points in a point pattern to the nearest line segment, use distfun or one of the low-level functions nncross or project2segment.

See Also

distmap, distmap.owin, distmap.ppp, distfun, nncross, nearestsegment, project2segment.

Examples

    a <- psp(runif(20),runif(20),runif(20),runif(20), window=owin())
    Z <- distmap(a)
    plot(Z)
    plot(a, add=TRUE)