

pair {sgeostat}                              R Documentation

_P_a_i_r _O_b_j_e_c_t

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

     Create a pair object from a point object.

     A pair object contains information defining pairs of
     points contained in a point object. A pair object is a
     list containing five vectors: `from', `to', `lags',
     `dist', and `bins'. The length of each of these vectors
     (except `bins') is equal to the number of pairs of
     points being represented, say k. The vectors `from' and
     `to' contain pointers into the vectors of a point
     object, pointing to each member of the pair of points
     (e.g., from[k] points to si and to[k] points to sj).
     The vector `dist' contains the distance between the
     pairs of points. The vector `lags' contains the lag
     number to which each pair of points has been assigned.
     The vector `bins' contains the spatial midpoint between
     each lag and is used for plotting.

_U_s_a_g_e_:

     pair(point.obj,num.lags=10,type='isotropic', theta=0, dtheta=5, maxdist)

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

point.obj: a point object generated by `point()'

num.lags: the number of lags into which to divide the pairs
          of points in the pair object. The lags are all of
          equal size.

    type: either ` object. If `'anisotropic'', then the
          arguments `theta' and `dtheta' are used to deter-
          mine which pairs of points to include.

   theta: an angle, measured in degrees from the horizontal
          x axis, that determines pairs of points to be
          included in the `pair' object (see Notes below).

  dtheta: a tolerance angle, around `theta', measured in
          degrees that determines pairs of points to be
          included in the `pair' object (see Notes below).

 maxdist: the distance beyond which not to consider pairs of
          points. A large number of spatial locations can
          cause the `pair' function to consume a consider-
          able amount of computation time. In most cases,
          spatial dependence can be adaquately characterized
          without examining the entire spaital extent of the
          data set.

_V_a_l_u_e_:

     A `pair' object:

    from: vector of indices into the point object for "from"
          point

      to: vector of indices into the point object for "to"
          point

    lags: vector of spatial lags of each pair

    dist: vector of distances between each pair

    bins: vector of spatial midpoints of each lag (used for
          plotting)

_N_O_T_E_:

     Name of this function changed from `pairs' to `pair' to
     avoid conflicts with R's `pairs' function!!

_N_o_t_e_:

     When creating an anisotropic pair object, the assump-
     tion is that the direction, as well as the distance,
     between pairs of points is important in describing the
     variation. Using the theta and dtheta arguments, pairs
     of points that meet direction requirements can be
     selected. A pair of points will be included when the
     angle between the positive x axis and the vector formed
     by the pair of points falls within the tolerance angle
     given by (theta-dtheta,theta+dtheta)

_R_e_f_e_r_e_n_c_e_s_:

     http://www.gis.iastate.edu/SGeoStat/homepage.html

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

     `point'

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

     maas.pair   <- pair(maas.point,num.lags=10,maxdist=2000)
     maas.pair25 <- pair(maas.point,num.lags=10,type='anisotropic',
                           theta=25,maxdist=500)

