gridcentres             package:spatstat             R Documentation

_R_e_c_t_a_n_g_u_l_a_r _g_r_i_d _o_f _p_o_i_n_t_s

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

     Generates a rectangular grid of points in a window

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

      gridcentres(window, nx, ny)

_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 points in each row of the rectangular grid. 

      ny: Number of points in each column of the rectangular grid. 

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

     This function creates a rectangular grid of points in the window.

     The bounding rectangle of the `window' is divided into a regular
     nx * ny grid of rectangular tiles. The function returns the x,y
     coordinates of the centres of these tiles.

     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') and for other miscellaneous purposes.

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

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

_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', `stratrand'

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


       library(spatstat)

       w <- unit.square()
       xy <- gridcentres(w, 10,15)

       plot(w)
       points(xy)


       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 <- gridcentres(w, 30, 30)
       ok <- inside.owin(xy$x, xy$y, w)

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


