spatstat (version 1.56-1)

integral.im: Integral of a Pixel Image

Description

Computes the integral of a pixel image.

Usage

integral(f, domain=NULL, …)
# S3 method for im
integral(f, domain=NULL, …)

Arguments

f

A pixel image (object of class "im") with pixel values that can be treated as numeric or complex values.

domain

Optional. Window specifying the domain of integration. Alternatively a tessellation.

…

Ignored.

Value

A single numeric or complex value (or a vector of such values if domain is a tessellation).

Details

The function integral is generic, with methods for "im", "msr", "linim" and "linfun".

The method integral.im treats the pixel image f as a function of the spatial coordinates, and computes its integral. The integral is calculated by summing the pixel values and multiplying by the area of one pixel.

The pixel values of f may be numeric, integer, logical or complex. They cannot be factor or character values.

The logical values TRUE and FALSE are converted to 1 and 0 respectively, so that the integral of a logical image is the total area of the TRUE pixels, in the same units as unitname(x).

If domain is a window (class "owin") then the integration will be restricted to this window. If domain is a tessellation (class "tess") then the integral of f in each tile of domain will be computed.

See Also

eval.im, [.im

Examples

# NOT RUN {
   # approximate integral of f(x,y) dx dy
   f <- function(x,y){3*x^2 + 2*y}
   Z <- as.im(f, square(1))
   integral.im(Z)
   # correct answer is 2

   D <- density(cells)
   integral.im(D)
   # should be approximately equal to number of points = 42

   # integrate over the subset [0.1,0.9] x [0.2,0.8]
   W <- owin(c(0.1,0.9), c(0.2,0.8))
   integral.im(D, W)
# }