Extract the pixel values of a pixel image at each point along a linear transect.
transect.im(X, ..., from="bottomleft", to="topright",
nsample=512, click=FALSE, add=FALSE, curve=NULL)An object of class "fv" which can be plotted.
A pixel image (object of class "im").
Ignored.
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.
Integer. Number of sample locations along the transect.
Optional.
Logical value.
If TRUE, the linear transect is determined interactively
by the user, who clicks two points on the current plot.
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).
Optional. A specification of a curved transect. See the section on Curved Transect.
If curve is given, then the transect will be a curve.
The argument curve should be a list with the following
arguments:
A function in the R language with one argument t.
A numeric vector of length 2 giving the range of values
of the argument t.
(Optional) a character string giving the symbolic name
of the function argument t; defaults to "t".
(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.
Adrian Baddeley Adrian.Baddeley@curtin.edu.au and Rolf Turner rolfturner@posteo.net
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.
im
Z <- bei.extra$elev
plot(transect.im(Z))
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