readAsciiGrid            package:maptools            R Documentation

_r_e_a_d/_w_r_i_t_e _t_o/_f_r_o_m (_E_S_R_I) _a_s_c_i_i_g_r_i_d _f_o_r_m_a_t

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

     read/write to/from ESRI asciigrid format; a fuzz factor has been
     added to 'writeAsciiGrid' to force cell resolution to equality if
     the difference is less than the square root of machine precision

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

      
     readAsciiGrid(fname, as.image = FALSE, plot.image = FALSE, 
      colname = basename(fname), proj4string = CRS(as.character(NA)), 
      dec=options()$OutDec)
     writeAsciiGrid(x, fname, attr = 1, na.value = -9999, dec=options()$OutDec, ...)

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

   fname: file name 

as.image: logical; if TRUE, a list is returned, ready to be shown with
          the 'image' command; if FALSE an object of class
          SpatialGridDataFrame-class is returned 

plot.image: logical; if TRUE, an image of the map is plotted

 colname: alternative name for data column if not file basename

proj4string: A CRS object setting the projection arguments of the
          Spatial Grid returned

     dec: decimal point character.  This should be a character string
          containing just one single-byte character - see note below.

       x: object of class SpatialGridDataFrame

    attr: attribute column; if missing, the first column is taken; a
          name or a column number may be given

na.value: numeric; value given to missing valued cells in the resulting
          map

     ...: arguments passed to write.table, which is used to write the
          numeric data 

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

     'readAsciiGrid' returns the grid map read; either as an object of
     class SpatialGridDataFrame-class or, if as.image is TRUE, as list
     with components 'x', 'y' and 'z'.

_N_o_t_e:

     In ArcGIS 8, it was not in general necessary to set the 'dec'
     argument; it is not necessary in a mixed environment with ArcView
     3.2 (R writes and ArcView reads "."), but inter-operation with
     ArcGIS 9 requires care because the defaults used by ArcGIS seem to
     be misleading, and it may be necessary to override what appear to
     be platform defaults by setting the argument.

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

     Edzer J. Pebesma, e.pebesma@geo.uu.nl

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

     as.image.SpatialGridDataFrame, image

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

     x <- readAsciiGrid(system.file("grids/test.ag", package="maptools")[1])
     summary(x)
     image(x)
     xp <- as(x, "SpatialPixelsDataFrame")
     abline(h=332000, lwd=3)
     xpS <- xp[coordinates(xp)[,2] < 332000,]
     summary(xpS)
     xS <- as(xpS, "SpatialGridDataFrame")
     summary(xS)
     tmpfl <- paste(tempdir(), "testS.ag", sep="/")
     writeAsciiGrid(xS, tmpfl)
     axS <- readAsciiGrid(tmpfl)
     opar <- par(mfrow=c(1,2))
     image(xS, main="before export")
     image(axS, main="after import")
     par(opar)
     unlink(tmpfl)

