variog4                 package:geoR                 R Documentation

_C_o_m_p_u_t_e_s _D_i_r_e_c_t_i_o_n_a_l _V_a_r_i_o_g_r_a_m_s

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

     Computes directional variograms for 4 directions provided by the
     user.

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

     variog4(geodata, coords = geodata$coords, data = geodata$data, 
             uvec = "default", breaks = "default", trend = "cte", lambda = 1,
             option = c("bin", "cloud", "smooth"),
             estimator.type = c("classical", "modulus"), 
             nugget.tolerance, max.dist, pairs.min = 2,
             bin.cloud = FALSE, direction = c(0, pi/4, pi/2, 3*pi/4), tolerance = pi/8,
             unit.angle = c("radians", "degrees"), messages, ...)

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

 geodata: a list containing element 'coords' as described next.
          Typically an object of the class '"geodata"' - a 'geoR'
          data-set. If not provided the arguments 'coords' must be
          provided instead.  

  coords: an n x 2 matrix containing coordinates of the n data
          locations in each row. Defaults to 'geodata$coords', if
          provided.

    data: a vector or matrix with data values. If a matrix is provided,
          each column is regarded as one variable or realization.
          Defaults to 'geodata$data', if provided.

    uvec: a vector with values to define the variogram binning. For
          further details see documentation for 'variog'.  

  breaks: a vector with values to define the variogram binning. For
          further details see documentation for 'variog'.  

   trend: specifies the mean part of the model. The options are:
          '"cte"' (constant mean), '"1st"' (a first order polynomial on
          the coordinates), '"2nd"' (a second order polynomial on the
          coordinates), or a formula of the type '~X' where 'X' is a
          matrix with the covariates (external trend). Defaults to
          '"cte"'.  

  lambda: values of the Box-Cox transformation parameter. Defaults to 1
          (no transformation). If another value is provided the
          variogram is computed after transforming the  data. A case of
          particular interest is lambda = 0 which corresponds to
          log-transformation.  

  option: defines the output type: the options '"bin"' returns values
          of binned variogram, '"cloud"' returns the variogram cloud
          and '"smooth"' returns the kernel smoothed variogram.
          Defaults to '"bin"'.

estimator.type: '"classical"' computes the classical method of moments
          estimator.  '"modulus"' returns the variogram estimator
          suggested by Hawkins and Cressie (see Cressie, 1993, pg 75).
          Defaults to '"classical"'.  

nugget.tolerance: a numeric value. Points which are separated by a
          distance less than this value are considered co-located.
          Defaults to zero.  

max.dist: a numerical value defining the maximum distance for the
          variogram. Pairs of locations separated for distance larger
          than this value are ignored for the variogram calculation.
          Defaults to the maximum distance among the pairs of data
          locations.  

pairs.min: a integer number defining the minimum numbers of pairs for
          the bins. For 'option = "bin"', bins with number of pairs
          smaller than this value are ignored. Defaults to 'NULL'.  

bin.cloud: logical. If 'TRUE' and 'option = "bin"' the cloud values for
          each class are included in the output. Defaults to 'FALSE'.  

direction: a vector with values of 4 angles, indicating the directions
          for which the variograms will be computed. Default
          corresponds to 'c(0, 45, 90, 135)' (degrees). 

tolerance: numerical value for the tolerance angle, when computing
          directional variograms. The value must be in the interval [0,
          90] degrees.  Defaults to pi/8.  

unit.angle: defines the unit for the specification of angles in the two
          previous arguments. Options are '"degrees"' and '"radians"'. 

messages: logical. Indicates whether status messages should be printed
          on the screen (or output device) while the function is
          running.  

     ...: arguments to be passed to the function 'ksmooth', if 'option
          = "smooth"'.  

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

     The output is an object of the class 'variog4', a list with five
     components. The first four elements are estimated variograms for
     the directions provided and the last is the omnidirectional
     variogram.  Each individual component is an object of the class
     'variogram', an output of the function 'variog'.

_A_u_t_h_o_r(_s):

     Paulo J. Ribeiro Jr. paulojus@leg.ufpr.br, 
      Peter J. Diggle p.diggle@lancaster.ac.uk.

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

     Further information on the package 'geoR' can be found at:
      <URL: http://www.leg.ufpr.br/geoR>.

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

     'variog' for variogram calculations and 'plot.variog4' for
     plotting results

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

     var4 <- variog4(s100, max.dist=1)
     plot(var4)

