r.slope.aspect(1)	      Grass User's Manual	     r.slope.aspect(1)



NNAAMMEE
       _r_._s_l_o_p_e_._a_s_p_e_c_t  -  Generates raster map layers of slope, aspect, curva-
       tures and partial derivatives from a raster map layer of true elevation
       values. Aspect is calculated counterclockwise from east.

       _(_G_R_A_S_S _R_a_s_t_e_r _P_r_o_g_r_a_m_)



SSYYNNOOPPSSIISS
       rr..ssllooppee..aassppeecctt

       rr..ssllooppee..aassppeecctt hheellpp

       rr..ssllooppee..aassppeecctt  [--aaqq]  eelleevvaattiioonn==_n_a_m_e  [ssllooppee==_n_a_m_e] [aassppeecctt==_n_a_m_e] [ffoorr--
       mmaatt==_n_a_m_e]  [zzffaaccttoorr==_v_a_l_u_e]   [pprreecc=_n_a_m_e_]    [ppccuurrvv=_n_a_m_e]   [ttccuurrvv=_n_a_m_e_]
       [ddxx=_n_a_m_e]      [ddyy=_n_a_m_e]      [ddxxxx=_n_a_m_e]      [ddyyyy=_n_a_m_e]     [ddxxyy=_n_a_m_e]
       [mmiinn__ssllpp__aalllloowweedd=_v_a_l_u_e]



DDEESSCCRRIIPPTTIIOONN
       rr..ssllooppee..aassppeecctt generates raster maps of slope, aspect,  curvatures  and
       first  and  second order partial derivatives from a raster map layer of
       true elevation values. The user must specify the input  _e_l_e_v_a_t_i_o_n  file
       name  and  at least one output file name. The user can also specify the
       _f_o_r_m_a_t for slope (degrees, percent; default=degrees), and _z_f_a_c_t_o_r: mul-
       tiplicative factor to convert elevation units to meters; (default 1.0).



OOPPTTIIOONNSS
       The program will be run non-interactively if the user specifies program
       inputs  and  any  desired  options  on the command line, using the form
       rr..ssllooppee..aassppeecctt [--aaqq] eelleevvaattiioonn==_n_a_m_e  [ssllooppee==_n_a_m_e]  [aassppeecctt==_n_a_m_e]  [ffoorr--
       mmaatt==_n_a_m_e]   [zzffaaccttoorr==_v_a_l_u_e]   [pprreecc=_n_a_m_e_]    [ppccuurrvv=_n_a_m_e]  [ttccuurrvv=_n_a_m_e_]
       [ddxx=_n_a_m_e]     [ddyy=_n_a_m_e]	    [ddxxxx=_n_a_m_e]	    [ddyyyy=_n_a_m_e]	    [ddxxyy=_n_a_m_e]
       [mmiinn__ssllpp__aalllloowweedd=_v_a_l_u_e]

       If the user runs: rr..ssllooppee..aassppeecctt

       without	command  line  arguments, the program will prompt the user for
       flag settings and parameter values.

   FFllaaggss::
       --aa  Do not align the settings of  the  current  geographic  region  (to
	   which  the output slope and aspect map layers will be set) to those
	   of the elevation layer. See NOTES.

       --qq  Run quietly, and suppress the printing of  information  on  program
	   operations during execution.


   PPaarraammeetteerrss::
       eelleevvaattiioonn==_n_a_m_e
	   Name of the raster map layer of true elevation values to be used as
	   input.

       ssllooppee==_n_a_m_e
	   Name of a raster map layer of slope values created from the	eleva-
	   tion map.

       aassppeecctt==_n_a_m_e
	   Name of a raster map layer of aspect values created from the eleva-
	   tion map.

       ffoorrmmaatt=name
	   format for reporting the slope; options: degrees,percent;  default:
	   degrees.

       zzffaaccttoorr==_v_a_l_u_e
	   Multiplicative   factor   to  convert  elevation  units  to	meters
	   (default: 1.0).

       ppccuurrvv ==_n_a_m_e
	   Output profile curvature filename

       ttccuurrvv ==_n_a_m_e
	   Output tangential curvature filename

       ddxx==_n_a_m_e
	   Output E-W slope filename

       ddyy==_n_a_m_e
	   Output N-S slope filename

       ddxxxx==_n_a_m_e
	   Output partial derivative dxx filename

       ddyyyy==_n_a_m_e
	   Output partial derivative dyy filename

       ddxxyy ==_n_a_m_e
	   Output partial derivative dxy filename

       mmiinn__ssllpp__aalllloowweedd =_v_a_l_u_e
	   Minimum slope value (in percent)  for  which  aspect  is  computed.
	   (default: 0.0)

       pprreecc=_n_a_m_e
	   type   of  output  aspect  and  slope  maps	options:  default,dou-
	   ble,float,int

       The raster _e_l_e_v_a_t_i_o_n map layer specified by the user must contain  true
       elevation values, _n_o_t rescaled or categorized data.

       The  raster  _a_s_p_e_c_t  map layer which is created indicates the direction
       that slopes are facing. The  aspect  categories	represent  the	number
       degrees	of east. Category and color table files are also generated for
       the aspect map  layer.  The  aspect  categories	represent  the	number
       degrees of east and they increase counterclockwise: 90deg is North, 180
       is West, 270 is South and 360 is East.

       The resulting raster _s_l_o_p_e map layer will contain slope values,	stated
       in  degrees of inclination from the horizontal if _f_o_r_m_a_t=degrees option
       (which is also default ) is chosen, and in percent rise if  _f_o_r_m_a_t=per-
       cent  option  is chosen. The category file, but not the color table, is
       generated by _r_._s_l_o_p_e_._a_s_p_e_c_t for the raster slope map layer.Profile  and
       tangential  curvatures  are the curvatures in the direction of steepest
       slope and in the direction of the contour tangent respectively.

       For some applications, the user will wish to  use  a  reclassified  map
       layer  of slope that groups slope values into ranges of slope. This can
       be done using _r_._r_e_c_l_a_s_s. An example of  a  useful  reclassification  is
       given below:
			    (in degrees)    (in percent)

		    1	      0-  1		0-  2%
		    2	      2-  3		3-  5%
		    3	      4-  5		6- 10%
		    4	      6-  8	       11- 15%
		    5	      9- 11	       16- 20%
		    6	     12- 14	       21- 25%
		    7	     15- 90	       26% and higher

	    The following color table works well with the above
	    reclassification.

		 category   red   green   blue

		    0	    179    179	   179
		    1	      0    102	     0
		    2	      0    153	     0
		    3	    128    153	     0
		    4	    204    179	     0
		    5	    128     51	    51
		    6	    255      0	     0
		    7	      0      0	     0



       NNOOTTEESS
       To  ensure  that  the raster elevation map layer is not inappropriately
       resampled,
       the settings for the current region are modified slightly (for the exe-
       cution
       of the program only): the resolution is set to match the resolution of
       the  elevation  map and the edges of the region (i.e. the north, south,
       east
       and west) are shifted, if necessary, to line  up  along	edges  of  the
       nearest
       cells in the elevation map. If the user really wants the elevation map
       resampled to the current region resolution, the -a flag should be spec-
       ified.

       The current mask, if set, is ignored.

       The algorithm used to determine slope and aspect uses a	3x3  neighbor-
       hood
       around  each  cell  in  the elevation file. Thus, it is not possible to
       determine
       slope and aspect for the cells adjacent to the edges in	the  elevation
       map
       layer. These cells are assigned a "no data" value (category 0) in both
       the slope and aspect raster map layers.

       Horn's formula is used to find the derivatives in x and y directions.

       Only when using integer elevation models, the aspect is biased in 0,
       45, 90, 180, 225, 270, 315, and 360 directions; i.e., the distribution
       of aspect categories is very uneven, with peaks at 0, 45,..., 360 cate-
       gories.

       Because most cells with a very small slope end up having category 0,
       45,..., 360 it is sometimes possible to reduce bias in these directions
       by filtering out computation of aspect in areas where terrain is almost
       flat. The new option

       mmiinn__ssllpp=_v_a_l_u_e

       was added (minimum slope for which aspect is computed). The aspect for
       all cells with slope < min_slp is set to 0 (no value).

       When working with floating point elevation models, no such aspect bias
       occurs.


       WWAARRNNIINNGG
       _(_t_h_e _f_o_l_l_o_w_i_n_g _m_a_y _n_o_t _b_e _t_r_u_e _a_n_y_m_o_r_e _b_e_c_a_u_s_e _o_f _i_n_t_r_o_d_u_c_t_i_o_n _o_f _N_U_L_L_,
       _b_u_t _i_t _h_a_s _n_o_t _b_e_e_n _t_e_s_t_e_d_)

       Elevations of zero (as well as below sea level elevations) are valid.
       This  means  that  areas  assigned category value 0 may have one of two
       possible
       meanings: they may either be areas of "no data" or areas having 0  ele-
       vation.

       If the user wishes _r_._s_l_o_p_e_._a_s_p_e_c_t to assume that cells assigned
       category value zero in the elevation map layer represent true elevation
       values, not areas of "no data", the user should set the	-z  flag  when
       running
       this program.

       If the -z flag is not set and the raster map layer of true elevation
       contains areas of "no data" that are assigned to category 0, either at
       its  edges  or  in  its	interior,  incorrect (and usually quite large)
       slopes
       will result.


       RREEFFEERREENNCCEE
       Horn, B. K. P. (1981). Hill Shading and the Reflectance	Map,  Proceed-
       ings
       of the IEEE, 69(1):14-47.


       SSEEEE AALLSSOO
       _r_._m_a_p_c_a_l_c

       _r_._n_e_i_g_h_b_o_r_s

       _r_._r_e_c_l_a_s_s

       _r_._r_e_s_c_a_l_e


       AAUUTTHHOORRSS
       Michael Shapiro, U.S.Army Construction Engineering Research Laboratory

       Olga Waupotitsch, U.S.Army Construction Engineering Research Laboratory

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_0_1_/_2_5 _0_5_:_4_5_:_3_4 _$



GRASS 5.0						     r.slope.aspect(1)
