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:

       w <- unit.square()
       xy <- stratrand(w, 10, 10)
       ## Not run: 
       plot(w)
       points(xy)
       
     ## End(Not run)

       # 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)
       ## Not run: 
       plot(w)
       points(xy)
       
     ## End(Not run)
       # determine which grid points are inside polygon
       ok <- inside.owin(xy$x, xy$y, w)
       ## Not run: 
       plot(w)
       points(xy$x[ok], xy$y[ok])
       
     ## End(Not run)

