pair                package: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 ` 'isotropic'' or `'anisotropic''. If `'isotropic''
          then all n choose 2 possible pairs of points are represented
          in the pair object. If `'anisotropic'', then the arguments
          `theta' and `dtheta' are used to determine 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 considerable 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 assumption 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)

