spokes               package:spatstat               R Documentation

_S_p_o_k_e_s _p_a_t_t_e_r_n _o_f _d_u_m_m_y _p_o_i_n_t_s

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

     Generates a pattern of dummy points in a window, given a data
     point pattern. The dummy points lie on the radii of circles
     emanating from each data point.

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

      spokes(x, y, nrad = 3, nper = 3, fctr = 1.5, Mdefault = 1)

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

       x: Vector of x coordinates of data points, or a list with
          components 'x' and 'y', or a point pattern (an object of
          class 'ppp'). 

       y: Vector of y coordinates of data points.  Ignored unless 'x'
          is a vector. 

    nrad: Number of radii emanating from each data point. 

    nper: Number of dummy points per radius. 

    fctr: Scale factor. Length of largest spoke radius is 'fctr * M'
          where 'M' is the mean nearest neighbour distance for the data
          points. 

Mdefault: Value of 'M' to be used if 'x' has length 1. 

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

     This function is useful in creating dummy points for quadrature
     schemes (see 'quadscheme').

     Given the data points, the function creates a collection of 'nrad
     * nper * length(x)' dummy points.

     Around each data point '(x[i],y[i])' there are 'nrad * nper' dummy
     points, lying on 'nrad' radii emanating from '(x[i],y[i])', with
     'nper' dummy points equally spaced along each radius.

     The (equal) spacing of dummy points along each radius is
     controlled by the factor 'fctr'.  The distance from a data point
     to the furthest of its associated dummy points is 'fctr * M' where
     'M' is the mean nearest neighbour distance for the data points.

     If there is only one data point the nearest neighbour distance is
     infinite, so the value 'Mdefault' will be used in place of 'M'.

     If 'x' is a point pattern, then the value returned is also a point
     pattern, which is clipped to the window of 'x'.  Hence there may
     be fewer than 'nrad * nper * length(x)' dummy points in the
     pattern returned.

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

     If argument 'x' is a point pattern, a point pattern with window
     equal to that of 'x'.  Otherwise a list with two components 'x'
     and 'y'.  In either case the components 'x' and 'y' of the value
     are numeric vectors giving the coordinates of the dummy 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',
     'stratrand'

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

       dat <- runifrect(10)
       ## Not run: 
       plot(dat)
       
     ## End(Not run)
       dum <- spokes(dat$x, dat$y)
       ## Not run: 
       points(dum$x, dum$y, pch=".")
       
     ## End(Not run)
       Q <- quadscheme(dat, dum)

