r.surf.contour(1)	      Grass User's Manual	     r.surf.contour(1)



NNAAMMEE
       rr..ssuurrff..ccoonnttoouurr	- Surface generation program from rasterized contours.
       _(_G_R_A_S_S _R_a_s_t_e_r _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       rr..ssuurrff..ccoonnttoouurr
       rr..ssuurrff..ccoonnttoouurr hheellpp
       rr..ssuurrff..ccoonnttoouurr [--ff] iinnppuutt==_n_a_m_e oouuttppuutt==_n_a_m_e

DDEESSCCRRIIPPTTIIOONN
       _r_._s_u_r_f_._c_o_n_t_o_u_r creates a raster elevation map from a rasterized contour
       map.   Elevation  values  are  determined using procedures similar to a
       manual methods.	To determine the elevation of a  point	on  a  contour
       map,  an  individual  might interpolate its value from those of the two
       nearest contour lines (uphill and downhill).


       _r_._s_u_r_f_._c_o_n_t_o_u_r works in a similar way.  Initially, a vector map of  the
       contour lines is made with the elevation of each line as its label (see
       _v_._d_i_g_i_t ).  When the program _v_._t_o_._r_a_s_t is run on the vector  map,  con-
       tinuous	"lines"  of rasters containing the contour line values will be
       the input for _r_._s_u_r_f_._c_o_n_t_o_u_r. For each cell in the  input  map,	either
       the cell is a contour line cell (which is given that value), or a flood
       fill is generated from that spot until the fill	comes  to  two	unique
       values.	So  the  _r_._s_u_r_f_._c_o_n_t_o_u_r  linearly interpolates between contour
       lines. The flood fill is not allowed to cross over the rasterized  con-
       tour  lines,  thus  ensuring  that an uphill and downhill contour value
       will be the two values chosen.  _r_._s_u_r_f_._c_o_n_t_o_u_r  interpolates  from  the
       uphill and downhill values by the true distance.


       The  program  will  be  run non-interactively if the user specifies the
       program parameter values and desired flag settings on the command line,
       using the form:


       rr..ssuurrff..ccoonnttoouurr [--ff] iinnppuutt==_n_a_m_e oouuttppuutt==_n_a_m_e



       Alternately,  the  user	can  simply type rr..ssuurrff..ccoonnttoouurr on the command
       line, without program arguments.   In  this  case,  the	user  will  be
       prompted  for needed inputs and option choices using the standard GRASS
       user interface described in the manual entry for _p_a_r_s_e_r .





   FFllaaggss::
       --ff     Invoke fast, but memory-intensive program operation.






   PPaarraammeetteerrss::
       iinnppuutt==_n_a_m_e
	      Name of an existing raster map layer that contains a set of ini-
	      tial  category  values  (i.e., some cells contain known category
	      values (denoting contours) while the rest contain zeros (0)).

       oouuttppuutt==_n_a_m_e
	      Name to be assigned to new output raster map layer  that	repre-
	      sents  a	smooth	(e.g.,	elevation)  surface generated from the
	      known category values in the input raster map layer.


NNOOTTEESS
       _r_._s_u_r_f_._c_o_n_t_o_u_r works well under the  following  circumstances:  1)  the
       contour lines extend to the the edge of the current region, 2) the pro-
       gram is run at the same resolution as that of the input map,  3)  there
       are  no disjointed contour lines, and 4) no spot elevation data BETWEEN
       contour lines exist.  Spot elevations at the tops of hills and the bot-
       toms  of  depressions,  on  the other hand, improve the output greatly.
       Violating these	constraints  will  cause  non-intuitive  anomalies  to
       appear in the output map.  Run _r_._s_l_o_p_e_._a_s_p_e_c_t
	on _r_._s_u_r_f_._c_o_n_t_o_u_r results to locate potential anomalies.


       The  running  of  _r_._s_u_r_f_._c_o_n_t_o_u_r is very sensitive to the resolution of
       rasterized vector map.  If multiple contour lines go through  the  same
       raster,	slight	anomalies  may	occur.	The speed of _r_._s_u_r_f_._c_o_n_t_o_u_r is
       dependent on how far "apart" the contour lines are from each other  (as
       measured  in  rasters).	Since a flood fill algorithm is used, the pro-
       gram's running time will grow exponentially with the  distance  between
       contour lines.


       _r_._s_u_r_f_._c_o_n_t_o_u_r

SSEEEE AALLSSOO
       _r_._s_u_r_f_._i_d_w

       _r_._s_u_r_f_._i_d_w_2

       _s_._s_u_r_f_._i_d_w

       _v_._d_i_g_i_t

       _v_._t_o_._r_a_s_t

       _r_._s_l_o_p_e_._a_s_p_e_c_t

       _p_a_r_s_e_r

AAUUTTHHOORR
       Chuck Ehlschlaeger, U.S. Army Construction Engineering Research Labora-
       tory



       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_0_1_/_2_5 _0_5_:_4_5_:_3_4 _$



GRASS 5.0						     r.surf.contour(1)
