transect.im {spatstat.explore}

Pixel Values Along a Transect

Description

Extract the pixel values of a pixel image at each point along a linear transect.

Usage

transect.im(X, ..., from="bottomleft", to="topright",
            nsample=512, click=FALSE, add=FALSE, curve=NULL)

Arguments

X

A pixel image (object of class "im").

...

Ignored.

from, to

Optional. Start point and end point of the transect. Pairs of (x,y) coordinates in a format acceptable to xy.coords, or keywords "bottom", "left", "top", "right", "bottomleft" etc.

nsample

Integer. Number of sample locations along the transect.

click

Optional. Logical value. If TRUE, the linear transect is determined interactively by the user, who clicks two points on the current plot.

add

Logical. If click=TRUE, this argument determines whether to perform interactive tasks on the current plot (add=TRUE) or to start by plotting X (add=FALSE).

curve

Optional. A specification of a curved transect. See the section on Curved Transect.

Details

The pixel values of the image X along a line segment will be extracted. The result is a function table ("fv" object) which can be plotted directly.

If click=TRUE, then the user is prompted to click two points on the plot of X. These endpoints define the transect.

Otherwise, the transect is defined by the endpoints from and to. The default is a diagonal transect from bottom left to top right of the frame.

Value

An object of class "fv" which can be plotted.

Curved Transect

If curve is given, then the transect will be a curve. The argument curve should be a list with the following arguments:

f

A function in the R language with one argument t.

tlim

A numeric vector of length 2 giving the range of values of the argument t.

tname

(Optional) a character string giving the symbolic name of the function argument t; defaults to "t".

tdescrip

(Optional) a character string giving a short description of the function argument t; defaults to "curve parameter".

The function f must return a 2-column matrix or data frame specifying the spatial coordinates (x,y) of locations along the curve, determined by the values of the input argument t.

Author(s)

Adrian Baddeley [e-mail] and Rolf Turner [e-mail]

See Also

im

Examples

  Z <- bei.extra$elev
  plot(transect.im(Z))