grtsarea              package:spsurvey              R Documentation

_S_e_l_e_c_t _G_R_T_S _S_a_m_p_l_e _o_f _a_n _A_r_e_a _R_e_s_o_u_r_c_e

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

     This function select a GRTS sample of an area resource.  This
     function uses hierarchical randomization to ensure that the sample
     will include no more than one point per cell and then picks a
     point in selected cells.

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

     grtsarea(shapefilename=NULL, areaframe, samplesize=100, SiteBegin=1,
        shift.grid=TRUE, startlev=NULL, maxlev=11, maxtry=1000, acept=1)

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

shapefilename: name of the input shapefile.  If shapefilename equals
          NULL, then the shapefile or shapefiles in the currrent
          directory are used. The default is NULL.

areaframe: a data frame containing id, mdcaty and mdm.

samplesize: number of points to select in the sample.  The default is
          100.

SiteBegin: number to use for first site in the design.  The default is
          1.

shift.grid: option to randomly shift the hierarchical grid, where TRUE
          means shift the grid and FALSE means do not shift the grid,
          which is useful if one desires strict spatial stratification
          by hierarchical grid cells.  The default is TRUE.

startlev: initial number of hierarchical levels to use for the GRTS
          grid, which must be less than or equal to maxlev (if maxlev
          is specified) and cannot be greater than 11.  The default is
          NULL.

  maxlev: maximum number of hierarchical levels to use for the GRTS
          grid, which cannot be greater than 11.  The default is 11.

  maxtry: maximum number of iterations for randomly generating a point
          The default is 1000.

   acept: parameter that controls peakedness of a center-peaked
          distribution, which must be between 0 and 1.  A value of 0
          gives a triangular distribution, and a value of 1 gives a
          uniform distribution.  The default is 1.

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

     A data frame of GRTS sample points containing: SiteID, id, x, y,
     mdcaty, and weight.

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

     Tony Olsen Olsen.Tony@epa.gov
      Tom Kincaid Kincaid.Tom@epa.gov

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

     Stevens, D.L., Jr., and A.R. Olsen. (2004). Spatially-balanced
     sampling of natural resources. _Journal of the American
     Statistical Association_, *99*, 262-278.

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

     'grts'

