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



NNAAMMEE
       _r_._s_u_n_m_a_s_k  -  calculate	cast  shadow  areas from sun position and DEM.
       Either A: exact sun position is specified, or B: date/time to calculate
       the sun position by r.sunmask itself.

       _(_G_R_A_S_S _R_a_s_t_e_r _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       rr..ssuunnmmaasskk [--zzvvss] eelleevv_=_n_a_m_e oouuttppuutt_=_n_a_m_e [aallttiittuuddee_=_v_a_l_u_e] [aazziimmuutthh_=_v_a_l_u_e]
       [yyeeaarr_=_v_a_l_u_e]  [mmoonntthh_=_v_a_l_u_e]  [ddaayy_=_v_a_l_u_e]  [hhoouurr_=_v_a_l_u_e]	[mmiinnuuttee_=_v_a_l_u_e]
       [sseeccoonndd_=_v_a_l_u_e] [ttiimmeezzoonnee_=_v_a_l_u_e] [eeaasstt_=_v_a_l_u_e] [nnoorrtthh_=_v_a_l_u_e]

DDEESSCCRRIIPPTTIIOONN
       _r_._s_u_n_m_a_s_k  creates  an  output  map  layer  based on an input elevation
       raster map layer and the sun position. The output  map  layer  contains
       the  cast  shadow areas arising from sun shine and elevations. The user
       can define the sun position either directly or the module calculates it
       from  given  location and date/time parameters using the NREL sun posi-
       tion algorithm. So either "A:"-parameters to specify  the  exact  known
       sun  position  or "B:-parameters" to specify date/time for sun position
       calculation by r.sunmask itself have to be used.

   FFllaagg::
       --zz     Zero is a real elevation

       --vv     verbose output

	      displays sun related information like sunset/sunrise etc.

       --ss     calculate sun position only and exit


   PPaarraammeetteerrss::
       eelleevv   Elevation raster map to be used for shadow calculation

       oouuttppuutt Name for the resulting binary cast shadow raster map (1=shadow)

       AA:: aallttiittuuddee
	      altitude of the sun above horizon, degrees (options: 0-89.999)

       AA:: aazziimmuutthh
	      azimuth of the sun from the north, degrees (options: 0-360)

       BB:: yyeeaarr
	      year (1950..2050) for sun position calculation

       BB:: mmoonntthh
	      month (0..12) for sun position calculation

       BB:: ddaayy day (0..31) for sun position calculation

       BB:: hhoouurr
	      hour (0..12) for sun position calculation

       BB:: mmiinnuuttee
	      minutes (0..60) for sun position calculation

       BB:: sseeccoonndd
	      seconds (0..60) for sun position calculation

       BB:: ttiimmeezzoonnee
	      timezone (east positive, offset from GMT,  also  use  to	adjust
	      daylight savings)

       eeaasstt   east coordinate (point of interest, default: map center)

       nnoorrtthh  north coordinate (point of interest, default: map center)

       The module performs sunset/sunrise checks and refraction correction for
       sun position  calculation.  Local  coordinate  systems  are  internally
       transformed  to latitude/longitude for the SOLPOS algorithm. The eleva-
       tion is not considered in the sunset/sunrise calculations.

NNootteess
       r.sunmask and daylight savings: Rather than convert time  to  GMT,  the
       solpos algorithm uses what is called Local Standard Time, which is gen-
       erally defined politically as an offset from GMT.  So the  key  is  the
       offset  from  GMT,  which  the solpos Time Zone parameter.  If the user
       specifies clock time (different for winter and  summer),  he/she  would
       have  to  change the Time Zone parameter seasonally in r.sunmask (time-
       zone parameter).


       Note: In latitude/longitude locations  the  position  coordinates  pair
       (east/west)  has  to be specified in decimal degree (not D:M:S). If not
       specified, the map center's coordinates will be used.  Also _g_._r_e_g_i_o_n _-_l
       displays the map center's coordinates.

AAcckknnoowwlleeddggeemmeennttss
       Acknowledgements: National Renewable Energy Laboratory for their SOLPOS
       2.0 sun position algorithm.

SSEEEE AALLSSOO
	_g_._r_e_g_i_o_n_, _r_._s_u_n_, _r_._s_l_o_p_e_._a_s_p_e_c_t

AAUUTTHHOORR
       Janne Soimasuo, Finland 1994

       update to FP by Huidae Cho 2001

       added solpos algorithm feature by Markus Neteler 2001



       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_3_/_0_3_/_2_8 _1_7_:_3_3_:_5_5 _$



GRASS 5.0							  r.sunmask(1)
