Centroid of a window

Description

Computes the centroid (centre of mass) of a window

Usage

 centroid.owin(w)

Arguments

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.

Value

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

Author(s)

Adrian Baddeley adrian@maths.uwa.edu.au http://www.maths.uwa.edu.au/~adrian/ and Rolf Turner rolf@math.unb.ca http://www.math.unb.ca/~rolf

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
  ## Not run: 
  plot(w)
  # plot the window
  points(centroid.owin(w))
  # mark its centroid 
  
## End(Not run)

  wapprox <- as.mask(w)
  # pixel approximation of window
  ## Not run: 
  points(centroid.owin(wapprox))
  # should be indistinguishable 
  
## End(Not run)