Evaluate Expression Involving Pixel Images
Evaluates any expression involving one or more pixel images, and returns a pixel image.
eval.im(expr, envir, harmonize=TRUE, warn=TRUE)
expr |
An expression. |
envir |
Optional. The environment in which to evaluate the expression, or a named list containing pixel images to be used in the expression. |
harmonize |
Logical. Whether to resolve inconsistencies between the pixel grids. |
warn |
Logical. Whether to issue a warning if the pixel grids were inconsistent. |
This function is a wrapper to make it easier to perform pixel-by-pixel calculations in an image.
Pixel images in spatstat
are represented by objects of class "im"
(see im.object). These are essentially matrices of
pixel values, with extra attributes recording the pixel dimensions,
etc.
Suppose X is a pixel image. Then eval.im(X+3)
will add 3 to the value of every pixel in X, and return
the resulting pixel image.
Suppose X and Y are two pixel images with compatible
dimensions: they have the same number of pixels, the same physical
size of pixels, and the same bounding box. Then
eval.im(X + Y) will add the corresponding pixel values in
X and Y, and return the resulting pixel image.
In general, expr can be any expression in the R language involving
(a) the names of pixel images, (b) scalar
constants, and (c) functions which are vectorised.
See the Examples.
First eval.im determines which of the variable names
in the expression expr refer to pixel images. Each such name
is replaced by a matrix containing the pixel values. The expression is
then evaluated. The result should be a matrix; it is taken as
the matrix of pixel values.
The expression expr must be vectorised.
There must be at least one pixel image in the expression.
All images must have compatible dimensions.
If harmonize=FALSE, images that are incompatible will cause an error.
If harmonize=TRUE, images that have incompatible dimensions
will be resampled so that they are compatible; if warn=TRUE,
a warning will be issued.
An image object of class "im".
Adrian Baddeley Adrian.Baddeley@curtin.edu.au and Rolf Turner r.turner@auckland.ac.nz
# test images
X <- as.im(function(x,y) { x^2 - y^2 }, unit.square())
Y <- as.im(function(x,y) { 3 * x + y }, unit.square())
eval.im(X + 3)
eval.im(X - Y)
eval.im(abs(X - Y))
Z <- eval.im(sin(X * pi) + Y)
## Use of 'envir': bei.extra is a list with components 'elev' and 'grad'
W <- eval.im(atan(grad) * 180/pi, bei.extra)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.