R: Pixel Values Along a Transect

transect.im {spatstat.core} | R Documentation

## 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 Adrian.Baddeley@curtin.edu.au and Rolf Turner r.turner@auckland.ac.nz

### See Also

`im`

### Examples

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

[Package spatstat.core version 2.4-4 Index]