CRS-class               package:rgdal               R Documentation

_C_l_a_s_s "_C_R_S" _o_f _c_o_o_r_d_i_n_a_t_e _r_e_f_e_r_e_n_c_e _s_y_s_t_e_m _a_r_g_u_m_e_n_t_s

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

     Interface class to the PROJ.4 projection system. The class is
     defined as an empty stub accepting value NA in the sp package. If
     the rgdal package is available, then the class will permit spatial
     data to be associated with coordinate reference systems

_O_b_j_e_c_t_s _f_r_o_m _t_h_e _C_l_a_s_s:

     Objects can be created by calls of the form 'CRS("projargs")',
     where "projargs" is a valid string of PROJ.4 arguments; the
     arguments must be entered exactly as in the PROJ.4 documentation,
     in particular there cannot be any white space in +<arg>=<value>
     strings, and successive such strings can only be separated by
     blanks. The initiation function calls the PROJ.4 library to verify
     the argument set against those known in the library, returning
     error messages where necessary. The complete argument set may be
     retrieved by examining the second list element returned by
     'validObject("CRS object")' to see which additional arguments the
     library will use (which assumptions it is making over and above
     submitted arguments). The function 'CRSargs()' can be used to show
     the expanded argument list used by the PROJ.4 library.

_S_l_o_t_s:


     '_p_r_o_j_a_r_g_s': Object of class '"character"': projection arguments;
          the arguments must be entered exactly as in the PROJ.4
          documentation, in particular there cannot be any white space
          in +<arg>=<value> strings, and successive such strings can
          only be separated by blanks. 

_M_e_t_h_o_d_s:


     _s_h_o_w 'signature(object = "CRS")': print projection arguments in
          object 

_N_o_t_e:

     Lists of projections may be seen by using the programs installed
     with the PROJ.4 library, in particular proj and cs2cs; with the
     latter, -lp lists projections, -le ellipsoids, -lu units, and -ld
     datum(s) known to the installed software (available in 'rgdal'
     using 'projInfo'). These are added to in successive releases, so
     tracking the website or compiling and installing the most recent
     revisions will give the greatest choice. Finding the very
     important datum transformation parameters to be given with the
     +towgs84 tag is a further challenge, and is essential when the
     datums used in data to be used together differ. Tracing projection
     arguments is easier now than before the mass ownership of GPS
     receivers raised the issue of matching coordinates from different
     argument sets (GPS output and paper map, for example).

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

     Roger Bivand Roger.Bivand@nhh.no

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

     <URL: http://proj.maptools.org/>

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

     CRSargs(CRS("+proj=longlat +datum=NAD27"))
     CRSargs(CRS("+init=epsg:4267"))
     CRSargs(CRS("+init=epsg:26978"))
     CRSargs(CRS("+proj=stere +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.999908 +x_0=155000 +y_0=463000 +ellps=bessel +towgs84=565.237,50.0087,465.658,-0.406857,0.350733,-1.87035,4.0812 +units=m"))
     # see http://trac.osgeo.org/gdal/ticket/1987
     CRSargs(CRS("+init=epsg:28992"))

