spatstat (version 1.31-3)

centroid.owin: Centroid of a window

Description

Computes the centroid (centre of mass) of a window

Usage

centroid.owin(w)

Arguments

w

A window

Value

• A list with components x, y giving the coordinates of the centroid of the window w.

Details

The centroid of the window w is computed. The centroid (``centre of mass'') is the point whose $x$ and $y$ coordinates are the mean values of the $x$ and $y$ coordinates of all points in the window.

The argument w should be a window (an object of class "owin", see owin.object for details) or can be given in any format acceptable to as.owin().

The calculation uses an exact analytic formula for the case of polygonal windows.

Note that the centroid of a window is not necessarily inside the window. If the window is convex then it does contain its centroid.

See Also

owin, as.owin

Examples

w <- owin(c(0,1),c(0,1))
  centroid.owin(w) 
  # returns 0.5, 0.5

  data(demopat)
  w <- demopat$window
  # an irregular window
  plot(w)
  # plot the window
  points(centroid.owin(w))
  # mark its centroid

  wapprox <- as.mask(w)
  # pixel approximation of window
  points(centroid.owin(wapprox))
  # should be indistinguishable
  <testonly>centroid.owin(w)
  centroid.owin(wapprox)</testonly>