polygrid                package:geoR                R Documentation

_C_o_o_r_d_i_n_a_t_e_s _o_f _P_o_i_n_t_s _I_n_s_i_d_e _a _P_o_l_y_g_o_n

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

     This function builds a rectangular grid and extracts points which
     are inside of an internal polygonal region.

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

     polygrid(xgrid, ygrid, poly, vec.inout = FALSE)

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

   xgrid: grid values in the x-direction.  

   ygrid: grid values in the y-direction.  

    poly: a matrix with the polygon coordinates.  

vec.inout: logical. If `TRUE' a logical vector is included in the
          output indicating whether each point of the grid is inside
          the polygon.  Defaults to `FALSE'.  

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

     This function requires the package `splancs'.

     The function works as follows: First it creates a grid using the R
     function `expand.grid' and then it uses the function `inout' from
     the package `splancs' to extract the points of the grid which are
     inside the polygon.

     Within the package geoR this function is typically used to select
     points in a non-rectangular region to perform spatial prediction
     using `krige.bayes', `krige.conv' or `ksline'. It is also useful
     to produce image or perspective plots of the prediction results.

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

     A list with components: 

  xypoly: an n x 2 matrix with the coordinates of the points inside the
          polygon.  

vec.inout: logical, a vector indicating whether each point of the
          rectangular grid is inside the polygon. Only returned if
          `vec.inout = TRUE'.  

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

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

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

     Further information about geoR can be found at:
     <URL: http://www.maths.lancs.ac.uk/~ribeiro/geoR.html>.

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

     `expand.grid', `inout. '

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

     poly <- matrix(c(.2, .8, .7, .1, .2, .1, .2, .7, .7, .1), ncol=2)
     plot(0:1, 0:1, type="n")
     lines(poly)
     poly.in <- polygrid(seq(0,1,l=11), seq(0,1,l=11), poly, vec=TRUE)
     points(poly.in$xy)

