as.im | R Documentation |
Converts various kinds of data to a pixel image
as.im(X, ...) ## S3 method for class 'im' as.im(X, W=NULL, ..., eps=NULL, dimyx=NULL, xy=NULL, na.replace=NULL) ## S3 method for class 'owin' as.im(X, W=NULL, ..., eps=NULL, dimyx=NULL, xy=NULL, na.replace=NULL, value=1) ## S3 method for class 'matrix' as.im(X, W=NULL, ...) ## S3 method for class 'tess' as.im(X, W=NULL, ..., eps=NULL, dimyx=NULL, xy=NULL, na.replace=NULL) ## S3 method for class 'function' as.im(X, W=NULL, ..., eps=NULL, dimyx=NULL, xy=NULL, na.replace=NULL, stringsAsFactors=NULL, strict=FALSE, drop=TRUE) ## S3 method for class 'funxy' as.im(X, W=Window(X), ...) ## S3 method for class 'expression' as.im(X, W=NULL, ...) ## S3 method for class 'distfun' as.im(X, W=NULL, ..., eps=NULL, dimyx=NULL, xy=NULL, na.replace=NULL, approx=TRUE) ## S3 method for class 'nnfun' as.im(X, W=NULL, ..., eps=NULL, dimyx=NULL, xy=NULL, na.replace=NULL, approx=TRUE) ## S3 method for class 'data.frame' as.im(X, ..., step, fatal=TRUE, drop=TRUE) ## Default S3 method: as.im(X, W=NULL, ..., eps=NULL, dimyx=NULL, xy=NULL, na.replace=NULL)
X |
Data to be converted to a pixel image. |
W |
Window object which determines the spatial domain and pixel array geometry. |
... |
Additional arguments passed to |
eps,dimyx,xy |
Optional parameters passed to |
na.replace |
Optional value to replace |
value |
Optional.
The value to be assigned to pixels inside the window,
if |
strict |
Logical value indicating whether to match formal arguments
of |
step |
Optional. A single number, or numeric vector of length 2, giving the grid step lengths in the x and y directions. |
fatal |
Logical value indicating what to do if the resulting image
would be too large for available memory. If |
drop |
Logical value indicating what to do if the result would
normally be a list of pixel images but the list contains
only one image.
If |
stringsAsFactors |
Logical value (passed to |
approx |
Logical value indicating whether to compute an approximate result at faster speed. |
This function converts the data X
into a pixel image
object of class "im"
(see im.object
).
The function as.im
is generic, with methods for the classes
listed above.
Currently X
may be any of the following:
a pixel image object, of class "im"
.
a window object, of class "owin"
(see
owin.object
). The result is an image
with all pixel entries equal to value
inside the window X
,
and NA
outside.
a matrix.
a tessellation (object of class "tess"
).
The result is a factor-valued image, with one factor level
corresponding to each tile of the tessellation. Pixels are classified
according to the tile of the tessellation into which they fall.
a single number (or a single logical, complex, factor or character
value). The result is an image
with all pixel entries equal to this constant value
inside the window W
(and NA
outside, unless the
argument na.replace
is given).
Argument W
is required.
a function of the form function(x, y, ...)
which is to be evaluated to yield the image pixel values.
In this case, the additional argument W
must be present.
This window will be converted to
a binary image mask. Then the function X
will be evaluated
in the form X(x, y, ...)
where x
and y
are
vectors containing the x and y coordinates
of all the pixels in the image mask, and ...
are any extra
arguments given. This function must return a
vector or factor of the same length as the input vectors,
giving the pixel values.
an object of class "funxy"
representing a
function(x,y,...)
defined in a spatial region.
The function will be evaluated as described above.
The window W
defaults to the domain of definition of the
function.
an object of class "funxy"
which also belongs to one of
the following special classes. If approx=TRUE
(the default),
the function will be evaluated approximately using a very fast
algorithm. If approx=FALSE
, the function will be evaluated
exactly at each grid location as described above.
an object of class "distfun"
representing a distance function
(created by the command distfun
).
The fast approximation is
the distance transform distmap
.
an object of class "nnfun"
representing a nearest neighbour function
(created by the command nnfun
).
The fast approximation is nnmap
.
an object of class "densityfun"
representing a kernel
estimate of intensity (created by
the command densityfun
).
The fast approximation is the Fast Fourier Transform
algorithm in density.ppp
.
an object of class "Smoothfun"
representing kernel-smoothed values
(created by the command Smoothfun
).
The fast approximation is the Fast Fourier Transform
algorithm in Smooth.ppp
.
An expression
involving the variables x
and y
representing the spatial coordinates, and possibly also involving other
variables.
The additional argument W
must be present; it will be converted to
a binary image mask. The expression X
will be evaluated
in an environment where x
and y
are
vectors containing the spatial coordinates
of all the pixels in the image mask.
Evaluation of the expression X
must yield a vector or factor,
of the same length as x
and y
, giving the pixel values.
a list with entries x, y, z
in the format expected by
the standard R
functions
image.default
and contour.default
.
That is, z
is a matrix of pixel values, x
and y
are vectors of x and y coordinates respectively,
and z[i,j]
is the pixel value for the location
(x[i],y[j])
.
a point pattern (object of class "ppp"
).
See the separate documentation for as.im.ppp
.
A data frame with at least three columns.
Columns named x
, y
and z
, if present,
will be assumed to contain the spatial coordinates and the pixel
values, respectively. Otherwise the x
and y
coordinates will be taken from the first two columns of the
data frame, and any remaining columns will be interpreted as
pixel values.
The spatial domain (enclosing rectangle) of the pixel image
is determined by the argument W
. If W
is absent,
the spatial domain is determined by X
.
When X
is a function, a matrix, or a single numerical value,
W
is required.
The pixel array dimensions of the final resulting image are determined by (in priority order)
the argument eps
, dimyx
or xy
if present;
the pixel dimensions of the window W
, if it is
present and if it is a binary mask;
the pixel dimensions of X
if it is an image,
a binary mask, or a list(x,y,z)
;
the default pixel dimensions,
controlled by spatstat.options
.
Note that if eps
, dimyx
or xy
is given, this will override
the pixel dimensions of X
if it has them.
Thus, as.im
can be used to change an image's pixel dimensions.
If the argument na.replace
is given, then all NA
entries
in the image will be replaced by this value. The resulting image is
then defined everwhere on the full rectangular domain, instead of a
smaller window. Here na.replace
should be a single value,
of the same type as the other entries in the image.
If X
is a pixel image that was created by an older version
of spatstat, the command X <- as.im(X)
will
repair the internal format of X
so that it conforms to the
current version of spatstat.
If X
is a data frame with m
columns,
then m-2
columns of data are interpreted as pixel values,
yielding m-2
pixel images. The result of
as.im.data.frame
is a list of pixel
images, belonging to the class "imlist"
.
If m = 3
and drop=TRUE
(the default), then the
result is a pixel image rather than a list containing this image.
If X
is a function(x,y)
which returns a matrix of
values, then as.im(X, W)
will be a list of pixel images.
A pixel image (object of class "im"
),
or a list of pixel images,
or NULL
if the conversion failed.
By default, if the pixel value data are character strings, they will be
treated as levels of a factor, and the resulting image will be
factor-valued. To prevent the conversion of character strings to
factors, use the argument stringsAsFactors=FALSE
,
which is recognised by most of the
methods for as.im
, or alternatively set
options(stringsAsFactors=FALSE)
.
The argument stringsAsFactors
is a logical value (passed to data.frame
)
specifying how to handle pixel values which
are character strings. If TRUE
, character values are
interpreted as factor levels. If FALSE
, they remain
as character strings. The default values of stringsAsFactors
depends on the version of R.
In R versions < 4.1.0
the factory-fresh default is stringsAsFactors=FALSE
and
the default can be changed by setting
options(stringsAsFactors=FALSE)
.
in R versions >= 4.1.0 the default
is stringsAsFactors=FALSE
and there is no option to
change the default.
Separate documentation for as.im.ppp
data(demopat) # window object W <- Window(demopat) plot(W) Z <- as.im(W) image(Z) # function Z <- as.im(function(x,y) {x^2 + y^2}, unit.square()) image(Z) # or as an expression Z <- as.im(expression(x^2+y^2), square(1)) # function with extra arguments f <- function(x, y, x0, y0) { sqrt((x - x0)^2 + (y-y0)^2) } Z <- as.im(f, unit.square(), x0=0.5, y0=0.5) image(Z) # Revisit the Sixties Z <- as.im(f, letterR, x0=2.5, y0=2) image(Z) # usual convention in R stuff <- list(x=1:10, y=1:10, z=matrix(1:100, nrow=10)) Z <- as.im(stuff) # convert to finer grid Z <- as.im(Z, dimyx=256) #' distance functions d <- distfun(redwood) Zapprox <- as.im(d) Zexact <- as.im(d, approx=FALSE) plot(solist(approx=Zapprox, exact=Zexact), main="") # pixellate the Dirichlet tessellation Di <- dirichlet(redwood) plot(as.im(Di)) plot(Di, add=TRUE, border="white") # as.im.data.frame is the reverse of as.data.frame.im grad <- bei.extra$grad slopedata <- as.data.frame(grad) slope <- as.im(slopedata) unitname(grad) <- unitname(slope) <- unitname(grad) # for compatibility all.equal(slope, grad) # TRUE ## handling of character values as.im("a", W=letterR, na.replace="b") as.im("a", W=letterR, na.replace="b", stringsAsFactors=FALSE)
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