r3.mapcalc(1)		      Grass User's Manual		 r3.mapcalc(1)



NNAAMMEE
       _r_3_._m_a_p_c_a_l_c - G3D grid volume data calculator.

       _(_G_R_A_S_S _3_D _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       rr33..mmaappccaallcc [rreessuulltt==_e_x_p_r_e_s_s_i_o_n]

DDEESSCCRRIIPPTTIIOONN
       _r_3_._m_a_p_c_a_l_c performs arithmetic on 3D grid volume data. New 3D grids can
       be created which  are  arithmetic  expressions  involving  existing  3D
       grids, floating point constants, and functions.

PPRROOGGRRAAMM UUSSEE
       If used without command line arguments, _r_3_._m_a_p_c_a_l_c will read its input,
       one line at a time, from standard input (which is the keyboard,	unless
       directed  from  a file or across a pipe).  Otherwise, the expression on
       the command line is evaluated. _r_3_._m_a_p_c_a_l_c expects its input to have the
       form:

       rreessuulltt==_e_x_p_r_e_s_s_i_o_n

       where _r_e_s_u_l_t is the name of a 3D grid to contain the result of the cal-
       culation and _e_x_p_r_e_s_s_i_o_n is any legal  arithmetic  expression  involving
       existing  3D grid, floating point constants, and functions known to the
       calculator. Parentheses are allowed in the expression and may be nested
       to any depth. _r_e_s_u_l_t will be created in the user's current mapset.

       The  formula  entered to _r_3_._m_a_p_c_a_l_c by the user is recorded both in the
       _r_e_s_u_l_t grid title (which appears in the category file for  _r_e_s_u_l_t)  and
       in the history file for _r_e_s_u_l_t.

       Some  characters have special meaning to the command shell. If the user
       is entering input to _r_._m_a_p_c_a_l_c on the command line, expressions	should
       be enclosed within single quotes. See NOTES, below.

OOPPEERRAATTOORRSS AANNDD OORRDDEERR OOFF PPRREECCEEDDEENNCCEE
       The following operators are supported:
	    -----------------------------------------------------------------------
	    %	       modulus (remainder upon division)   Arithmetic  4
	    /	       division 			   Arithmetic  4
	    *	       multiplication			   Arithmetic  4
	    +	       addition 			   Arithmetic  3
	    -	       subtraction			   Arithmetic  3
	    ==	       equal				   Logical     2
	    !=	       not equal			   Logical     2
	    >	       greater than			   Logical     2
	    >=	       greater than or equal		   Logical     2
	    <	       less than			   Logical     2
	    <=	       less than or equal		   Logical     2
	    &&	       and				   Logical     1
	    ||	       or				   Logical     1

       applied before those with lower precedence. Division by 0  and  modulus
       by
       0  are  acceptable  and give a 0 result. The logical operators give a 1
       result
       if the comparison is true, 0 otherwise.



       33DD GGRRIIDD NNAAMMEESS
       Anything in the expression which is not a number, operator, or function
       name is taken to be a 3D grid name. Examples:

       volume

       x3

       3d.his

       Most  GRASS raster map layers and 3D grids meet this naming convention.
       However, if a 3D grid has a name which conflicts with the  above  rule,
       it
       should be quoted. For example, the expression

       x = a-b

       would be interpreted as: x equals a minus b, whereas

       x = "a-b"

       would be interpreted as: x equals 3D grid named _a_-_b

       Also

       x = 3107

       would create _x filled with the number 3107, while

       x = "3107"

       would copy the 3D grid _3_1_0_7 to the 3D grid _x.

       Quotes are not required unless the 3D grid names look like numbers or
       contain	operators,  OR	unless	the  program is run non-interactively.
       Examples
       given here assume the program is run interactively. See NOTES, below.

       _r_3_._m_a_p_c_a_l_c will look for the 3D grids according to the user's
       current mapset search path. It is possible to override the search path
       and specify the mapset from which to select the 3D grid. This  is  done
       by
       specifying the 3D grid name in the form:

       name@mapset

       For example, the following is a legal expression:

       result = x@PERMANENT / y@SOILS

       The  mapset  specified  does  not have to be in the mapset search path.
       (This
       method of overriding the mapset search path is common to all GRASS com-
       mands,
       not just _r_3_._m_a_p_c_a_l_c.)


       TTHHEE NNEEIIGGHHBBOORRHHOOOODD MMOODDIIFFIIEERR
       3D grids are data base files stored in voxel format, i.e., three-dimen-
       sional
       matrices of float/double values. In _r_3_._m_a_p_c_a_l_c, 3D grids may be
       followed by a _n_e_i_g_h_b_o_r_h_o_o_d modifier that specifies a relative offset
       from the current cell being evaluated. The format is
       _m_a_p_[_r_,_c_,_d_],
       where _r is the row offset, _c is the column offset and _d
       is the depth offset. For example, _m_a_p_[_1_,_2_,_3_] refers to the cell
       one row below, two columns to the right and 3 levels below of the  cur-
       rent
       cell, _m_a_p_[_-_3_,_-_2_,_-_1_] refers to the cell three rows above, two columns
       to the left and one level below of the current cell, and _m_a_p_[_0_,_1_,_0_]
       refers  to  the	cell one column to the right of the current cell. This
       syntax
       permits the development of neighborhood-type filters within a single 3D
       grid or across multiple 3D grids.





       FFUUNNCCTTIIOONNSS
       The functions currently supported are listed in the table below.

       ---------------------------------------------------------------------------
       abs(x)		       return absolute value of x
       atan(x)		       inverse tangent of x (result is in degrees)
       cos(x)		       cosine of x (x is in degrees)
       col()		       return current column
       depth()		       return current depth
       eval([x,y,...,]z)       evaluate values of listed expr, pass results to
       z
       exp(x)		       exponential function of x
       exp(x,y) 	       x to the power y
       ewres()		       east-west resolution from WIND3D
       if		       decision options:
       if(x)		       1 if x not zero, 0 otherwise
       if(x,a)		       a if x not zero, 0 otherwise
       if(x,a,b)	       a if x not zero, b otherwise
       if(x,a,b,c)	       a if x > 0, b if x is zero, c if x < 0
       isnull(x)	       1 if x not zero, 0 otherwise
       log(x)		       natural log of x
       log(x,b) 	       log of x base b
       max(x,y[,z...])	       largest value of those listed
       median(x,y[,z...])      median value of those listed
       min(x,y[,z...])	       smallest value of those listed
       mode(x,y[,z...])        most frequently value of those listed
       null()		       return 0
       nsres()		       north-south resolution from WIND3D
       rand(x,y)	       random value between x and y
       round(x) 	       round x
       row()		       return current row
       sin(x)		       sine of x (x is in degrees)
       sqrt(x)		       square root of x
       tan(x)		       tangent of x (x is in degrees)
       tbres()		       top-bottom resolution from WIND3D
       x()		       return current x value
       y()		       return current y value
       z()		       return current z value
	Note, that the row(), col() and depth() indexing starts with 1.

EEXXAAMMPPLLEESS
       To compute the average of two 3D grids _a and _b:
       To form a weighted average:

       To produce a binary representation of 3D grid
       _a so that category
       0 remains 0 and all other categories become 1:

       This could also be accomplished by:

       To mask 3D grid _b by 3D grid _a:




       RREEGGIIOONN//MMAASSKK
       The  user  must	be  aware of the current geographic region and current
       mask
       settings when using _r_3_._m_a_p_c_a_l_c. All 3D grids are read into the current
       geographic region masked by the current mask. If it is desired to  mod-
       ify
       an  existing  3D  grid without involving other 3D grids, the geographic
       region
       should
       be set to agree with the cell header for the 3D grid. For example, sup-
       pose
       it is determined that the
       _v_o_l_u_m_e 3D grid must have each category
       value  increased  by  10  meters. The following expression is legal and
       will
       do the job:

       Since a category value of 0 is used in GRASS for locations which do not
       exist in 3D grid, the new 3D grid will contain the category value 10 in
       the locations that did not exist in the original volume. Therefore, in
       this example, it is essential that the  boundaries  of  the  geographic
       region
       be set to agree with the cell header.

       However,  if  there  is	a  current mask, then the resultant 3D grid is
       masked
       when it is written; i.e., 0 category values in the mask force zero val-
       ues
       in the output.


       NNOOTTEESS
       Extra  care  must  be  taken  if the expression is given on the command
       line.
       Some characters have special meaning to the UNIX shell. These include,
       among others:

       * ( ) > & |

       It is advisable to put single quotes around the expression; e.g.:

       Without the quotes, the *, which has special meaning to the UNIX shell,
       would be altered and _r_3_._m_a_p_c_a_l_c would see something other than the
       *.

       If the input comes directly from the keyboard and the _r_e_s_u_l_t
       3D grid exists, the user will be asked if it can be overwritten. Other-
       wise,
       the _r_e_s_u_l_t 3D grid will automatically be overwritten if it exists.

       Quoting _r_e_s_u_l_t is not allowed. However, it is never necessary
       to quote _r_e_s_u_l_t since it is always taken to be a 3D grid name.

       For formulas that the user enters from standard input (rather than from
       the command line), a line continuation feature now exists. If the user
       adds \ to the end of an input line, _r_3_._m_a_p_c_a_l_c assumes that the
       formula	being entered by the user continues on to the next input line.
       There is no limit to the possible number  of  input  lines  or  to  the
       length
       of a formula.

       If the _r_3_._m_a_p_c_a_l_c formula entered by the user is very long, the
       map  title  will  contain only some of it, but most (if not all) of the
       formula
       will be placed into the history file for the _r_e_s_u_l_t map.

       When the user enters input to _r_3_._m_a_p_c_a_l_c non-interactively on
       the command line, the program will not warn the user not  to  overwrite
       existing
       3D grids. Users should therefore take care to assign program outputs 3D
       grid file names that do not yet exist in their current mapsets.


       BBUUGGSS
       Continuation lines must end with a  and have NO	trailing  white  space
       (blanks
       or tabs). If the user does leave white space at the end of continuation
       lines, the error messages produced by _r_3_._m_a_p_c_a_l_c will be meaningless
       and the equation will not work as the user intended.

       Error messages produced by _r_3_._m_a_p_c_a_l_c are almost useless. In
       future,
       _r_3_._m_a_p_c_a_l_c should make some attempt to point the user to
       the offending section of the equation, e.g.:


	       ERROR: somewhere in line 1: ...	b ++ c ...
       Currently, there is no comment mechanism in _r_3_._m_a_p_c_a_l_c. Perhaps
       adding a capability that would cause the entire line to be ignored when
       the user inserted a # at the start of a line as if it were not present,
       would do the trick.

       The function should require the user to type "end" or "exit" instead
       of simply a blank line. This would make separation of multiple scripts
       separable by white space.




       SSEEEE AALLSSOO
       _r_._m_a_p_c_a_l_c


       AAUUTTHHOORR
       Tomas Paudits & Jaro Hofierka, funded by GeoModel s.r.o., Slovakia

       tpaudits@mailbox.sk,
       hofierka@geomodel.sk

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_0_1_/_2_5 _0_5_:_4_5_:_3_5 _$



GRASS 5.0							 r3.mapcalc(1)
