r.topidx(1)		      Grass User's Manual		   r.topidx(1)



NNAAMMEE
       rr..ttooppiiddxx  - creates topographic index, ln(a/tan(beta)), map from eleva-
       tion map

       _(_G_R_A_S_S _R_a_s_t_e_r _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       rr..ttooppiiddxx [[--oovv]] iinnppuutt_=_n_a_m_e oouuttppuutt_=_n_a_m_e

DDEESSCCRRIIPPTTIIOONN
       _r_._t_o_p_i_d_x creates topographic index, ln(a/tan(beta)), map from elevation
       map.


       where  a: the area of the hillslope per unit contour length that drains
       through any point


       tan(beta): the local  surface  topographic  slope  (delta  vertical)  /
       (delta horizontal)


       Elevation  map  need  not  to be rectangular if study basin was already
       determined.  Non-interesting region may have NULL values.  Study  basin
       map  can  be  taken  from  _r_._w_a_t_e_r_._o_u_t_l_e_t  then the following _r_._m_a_p_c_a_l_c
       statements will create study basin extracted elevation map.


       r.mapcalc "belev = if(isnull(basin), basin, elev)"


       _r_._a_v_g_s_t_a_t_s prints out averaged statistics for topographic index.

   FFllaaggss::
       --oo     Overwrite output map

       --vv     Output verbosely


   PPaarraammeetteerrss::
       iinnppuutt  Elevation map

       oouuttppuutt Topographic index ln(a/tanB) map


SSEEEE AALLSSOO
       _r_._t_o_p_m_o_d_e_l, _r_._w_a_t_e_r_._o_u_t_l_e_t, _r_._m_a_p_c_a_l_c

AAUUTTHHOORRSS
       Main algorithm sources are rewritten from GRIDATB.FOR.

       GRIDATB.FOR is available from www.es.lancs.ac.uk/hfdg/topmodel.html.
       Thanks to Keith Beven.


       GRASS port by Huidae Cho

       Hydro Laboratory, Kyungpook National University, South Korea

       _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.topidx(1)
