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



NNAAMMEE
       rr..ssuurrff..aarreeaa  - Surface area estimation for rasters.
       _(_G_R_A_S_S _R_a_s_t_e_r _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       rr..ssuurrff..aarreeaa
       rr..ssuurrff..aarreeaa hheellpp
       rr..ssuurrff..aarreeaa iinnppuutt==_n_a_m_e [vvssccaallee==_v_a_l_u_e]

DDEESSCCRRIIPPTTIIOONN
       _r_._s_u_r_f_._a_r_e_a  Calculates	area  of  regular 3D triangulated
       points (centers of cells)  in  current  region  by  adding
       areas  of  triangles.   Therefore,  area of a flat surface
       will be reported as (rows + cols -1)*(area of  cell)  less
       than area of flat region due to a half row and half column
       missing around the perimeter.


       NNOOTTEE::  This calculation is heavily dependent on data reso-
       lution  (think  of  it as a fractal shoreline problem, the
       more resolution the more  detail,  the  more  area,  etc).
       This  program uses the _C_U_R_R_E_N_T _G_R_A_S_S _R_E_G_I_O_N, not the reso-
       lution of the map.  This is especially important for  sur-
       faces  with  NULL  values and highly irregular edges.  The
       program does not [currently] attempt to	correct  for  the
       error introduced by this _e_d_g_e _e_f_f_e_c_t.


       This  version actually calculates area twice for each tri-
       angle pair, keeping a running  minimum  and  maximum  area
       depending on the direction of the diagonal used.


       Reported totals are:

	      "Plan" area of NULL values within the current GRASS
	      region

	      "Plan" area within  calculation  region  (rows-1	*
	      cols-1 * cellarea)

	      Average  of  the	minimum and maximum calculated 3d
	      triangle area within this region

	      "Plan" area within current  GRASS  region  (rows	*
	      cols * cellarea)

	      Scaling  of calculated area to current GRASS region
	      (see NOTE)



       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..aarreeaa iinnppuutt==_n_a_m_e [vvssccaallee==_v_a_l_u_e]



       Alternately, the user can simply type rr..ssuurrff..aarreeaa  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

   PPaarraammeetteerrss::
       iinnppuutt==_n_a_m_e
	      Name of an existing raster map layer to use for the
	      calculation.

       vvssccaallee==_v_a_l_u_e
	      Optional	vertical  scaling value to use in surface
	      area calculation.


NNOOTTEESS
       _r_._s_u_r_f_._a_r_e_a works best when the	surface  being	evaluated
       extends	to  the edges of the current GRASS region and the
       cell resolution is small.  Surfaces which  are  especially
       long  and  thin	and  have highly irregular boudaries will
       tend to have underestimated surface areas.  Setting a high
       cell  resolution  (small  area)	will  greatly reduce this
       impact, but will cause longer processing times.




       _r_._s_u_r_f_._a_r_e_a

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

       _r_._s_u_r_f_._f_r_a_c_t_a_l

       _r_._s_u_r_f_._g_a_u_s_s

       _v_._t_o_._r_a_s_t

       _r_._s_l_o_p_e_._a_s_p_e_c_t

       _g_._r_e_g_i_o_n

       _p_a_r_s_e_r

AAUUTTHHOORR
       Bill Brown, USACERL December 21, 1994


       Modified for floating point rasters  and  NULL  values  by
       Eric G. Miller (October 17, 2000)



       _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.area(1)
