Vertices of a Window

Description

Finds the vertices of a window

Usage

 vertices(w)

Arguments

Details

This function computes the vertices (`corners') of a spatial window.

The argument w should be a window (an object of class "owin", see owin.object for details).

If w is a rectangle, the coordinates of the four corner points are returned.

If w is a polygonal window (consisting of one or more polygons), the coordinates of the vertices of all polygons are returned.

If w is a binary mask, then a `boundary pixel' is defined to be a pixel inside the window which has at least one neighbour outside the window. The coordinates of the centres of all boundary pixels are returned.

Value

A list with components x and y giving the coordinates of the vertices.

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.object.

Examples

  data(letterR)
  vert <- vertices(letterR)

  plot(letterR, main="Polygonal vertices")
  points(vert)
  plot(letterR, main="Boundary pixels")
  points(vertices(as.mask(letterR)))