stratrand              package:spatstat              R Documentation

_S_t_r_a_t_i_f_i_e_d _r_a_n_d_o_m _p_o_i_n_t _p_a_t_t_e_r_n

_D_e_s_c_r_i_p_t_i_o_n:

     Generates a ``stratified random'' pattern of points in a window,
     by dividing the window into rectangular tiles and placing `k'
     random points in each tile.

_U_s_a_g_e:

      stratrand(window, nx, ny, k = 1)

_A_r_g_u_m_e_n_t_s:

  window: A window.  An object of class `owin', or data in any format
          acceptable to `as.owin()'. 

      nx: Number of tiles in each row. 

      ny: Number of tiles in each column. 

       k: Number of random points to generate in each tile. 

_D_e_t_a_i_l_s:

     The bounding rectangle of `window' is divided into a regular nx *
     ny grid of rectangular tiles. In each tile, `k' random points are
     generated independently with a uniform distribution in that tile. 

     Note that some of these grid points may lie outside the window, if
     `window' is not of type `"rectangle"'. The function `inside.owin'
     can be used to select those grid points which do lie inside the
     window. See the examples.

     This function is useful in creating dummy points for quadrature
     schemes (see `quadscheme') as well as in simulating random point
     patterns.

_V_a_l_u_e:

     A list with two components `x' and `y', which are numeric vectors
     giving the coordinates of the random points.

_A_u_t_h_o_r(_s):

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

_S_e_e _A_l_s_o:

     `quad.object', `quadscheme', `inside.owin', `gridcentres'

_E_x_a_m_p_l_e_s:


       library(spatstat)

       w <- unit.square()
       xy <- stratrand(w, 10, 10)

       plot(w)
       points(xy)


       # polygonal boundary
       bdry <- list(x=c(0.1,0.3,0.7,0.4,0.2),
                    y=c(0.1,0.1,0.5,0.7,0.3))
       w <- owin(c(0,1), c(0,1), poly=bdry)
       xy <- stratrand(w, 10, 10, 3)

       plot(w)
       points(xy)

       # determine which grid points are inside polygon
       ok <- inside.owin(xy$x, xy$y, w)

       plot(w)
       points(xy$x[ok], xy$y[ok])


