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 resolution (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 resolution of the map.  This  is  especially  important
       for  surfaces 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 triangle 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 * cel-
	      larea)

	      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	inter-
       face 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  calcula-
	      tion.


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

       _r_._v_o_l_u_m_e

       _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_: _$_D_a_t_e_: _2_0_0_2_/_1_2_/_1_1 _1_8_:_0_0_:_4_3 _$



GRASS 5.0							r.surf.area(1)
