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]    [ttiimmee--
       zzoonnee_=_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  out-
       put  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
       position  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/sun-
	      rise etc.

       --ss     calculate sun position only and exit


   PPaarraammeetteerrss::
       eelleevv   Elevation raster map to be used for shadow calcula-
	      tion

       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.

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


       Note: In latitude/longitude locations the position coordi-
       nates  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_: _$_D_a_t_e_: _2_0_0_2_/_0_3_/_0_1 _0_0_:_0_8_:_3_1 _$



GRASS 5.0					     r.sunmask(1)
