shade.rel.sh(1)        Grass User's Manual	  shade.rel.sh(1)



NNAAMMEE
       sshhaaddee..rreell..sshh   - Creates a shaded relief map based on cur-
       rent resolution settings and sun altitude and azimuth val-
       ues entered by the user.
       _(_G_R_A_S_S _S_h_e_l_l _S_c_r_i_p_t_)

SSYYNNOOPPSSIISS
       sshhaaddee..rreell..sshh
       sshhaaddee..rreell..sshh	hheellpp	 sshhaaddee..rreell..sshh	 [aallttiittuuddee==_v_a_l_u_e]
       [aazziimmuutthh==_v_a_l_u_e] [eelleevvaattiioonn==_n_a_m_e]

DDEESSCCRRIIPPTTIIOONN
       _s_h_a_d_e_._r_e_l_._s_h is a Bourne shell (sh(1)) script that creates
       a  raster  shaded  relief  map based on current resolution
       settings and on sun altitude and azimuth values entered by
       the  user.   The new shaded relief map is named _._s_h_a_d_e and
       stored in the user's current mapset.  The map is  assigned
       a grey-scale color table.


       In  case,  no parameter are provided on startup, this pro-
       gram  is  interactive;  the  user  enters   the	 command:
       sshhaaddee..rreell..sshh

       The program then prompts the user to enter values for:

	      the  altitude of the sun in degrees above the hori-
	      zon (a value between 0 and 90 degrees), and

	      the azimuth of the sun in degrees to  the  east  of
	      north (a value between -1 and 360 degrees).

	      the  name of a raster map layer whose cell category
	      values are to  provide  elevation  values  for  the
	      shaded  relief map.  Typically, this would be a map
	      layer of elevation;  however, any raster map  layer
	      can be named.

       Specifically,  _s_h_a_d_e_._r_e_l_._s_h  executes the following _r_._m_a_p_-
       _c_a_l_c statement:


       rr..mmaappccaallcc <<<< EEOOFF

	      $ELEV.shade = eval( \

	      x=($elev[-1,-1] + 2*$elev[0,-1] + $elev[1,-1] \

	      -$elev[-1,1]	  -	   2*$elev[0,1] 	-
	      $elev[1,1])/(8.*ewres()) , \

	      y=($elev[-1,-1] + 2*$elev[-1,0] + $elev[-1,1] \

	      -$elev[1,-1]	   -	    2*$elev[1,0]	-
	      $elev[1,1])/(8.*nsres()) , \

	      slope=90.-atan(sqrt(x*x + y*y)), \

	      a=round(atan(x,y)), \

	      a=if(isnull(a),1,a), \

	      aspect=if(x||y,if(a,a,360.)), \

	      cang = sin($alt)*sin(slope) +  cos($alt)*cos(slope)
	      * cos($az-aspect), \

	      if(cang < 0.,0.,100.*cang), \

	      if(isnull(cang), null(), 100.*cang))


       EOF




       Refer to the manual entry for _r_._m_a_p_c_a_l_c for an explanation
       of the filtering syntax shown  in  the  above  expression.
       See,  for  example, the section on "The Neighborhood Modi-
       fier".


       _s_h_a_d_e_._r_e_l_._s_h then runs _r_._c_o_l_o_r_s	to  assign  a  grey-scale
       color  table  to the new shaded relief map _._s_h_a_d_e, by exe-
       cuting the command:


       rr..ccoolloorrss sshhaaddee ccoolloorr==grey


FFIILLEESS
       This program is simply a shell script.  Users are  encour-
       aged  to  make their own shell scripts using similar tech-
       niques.	See $GISBASE/scripts/shade.rel.sh.

SSEEEE AALLSSOO
       _A_n _A_l_g_e_b_r_a  _f_o_r	_G_I_S  _a_n_d  _I_m_a_g_e  _P_r_o_c_e_s_s_i_n_g,  by  Michael
       Shapiro	and  Jim Westervelt, U.S. Army Construction Engi-
       neering Research Laboratory (March/1991) (get  from  GRASS
       web site).


       _b_l_e_n_d_._s_h

       _g_._a_s_k

       _g_._r_e_g_i_o_n

       _r_._c_o_l_o_r_s

       _r_._m_a_p_c_a_l_c _s_h_a_d_e_._c_l_r_._s_h

AAUUTTHHOORR
       Jim   Westervelt,   U.S.   Army	Construction  Engineering
       Research Laboratory

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_0_3_/_0_1 _0_0_:_0_8_:_3_1 _$



GRASS 5.0					  shade.rel.sh(1)
