NAME

       gensurf - generate a RADIANCE or Wavefront description of a curved surface

SYNOPSIS

       gensurf mat name 'x(s,t)' 'y(s,t)' 'z(s,t)' m n [ -e expr ][ -f file ][ -s ][ -o ]
       gensurf mat name 'x(s,t)' 'y(s,t)' dfile m n [ -e expr ][ -f file ][ -s ][ -o ]
       gensurf mat name dfile dfile dfile m n [ -s ][ -o ]

DESCRIPTION

       Gensurf  produces  either  a  RADIANCE scene description or a Wavefront .OBJ file of a functional surface
       defined by the parametric equations x(s,t), y(s,t), and z(s,t).  The surface normal  is  defined  by  the
       right  hand rule as applied to (s,t).  S will vary from 0 to 1 in steps of 1/m, and t will vary from 0 to
       1 in steps of 1/n.  The surface will be composed of 2*m*n or fewer  triangles  and  quadrilaterals.   The
       expressions are of the same type used in RADIANCE function files.  Auxiliary expressions and/or files may
       be  specified  in  any  number  of  -e  and  -f  options.   The  -s option adds smoothing (surface normal
       interpolation) to the surface.  The -o option produces a Wavefront .OBJ file rather than a RADIANCE scene
       description.  This is most useful as input to the obj2mesh(1) program for producing a compiled  mesh.   A
       single  "usemtl" statement will appear at the beginning of the .OBJ output, echoing the modifier given on
       the command line.

       Rough holes may be cut in the mesh by defining a valid(s,t) function.  Where this function  is  positive,
       polygon  vertices  will  be  produced.  Where it is negative, no geometry will be output.  Surface normal
       interpolation will ignore any invalid vertices.

       The second invocation form reads z data values from the file dfile.  This file must give  either  m*n  or
       (m+1)*(n+1) floating point z values.  If m*n values are given, then the values correspond to the centroid
       of  each  quadrilateral  region.   If  (m+1)*(n+1)  values  are  given, then the values correspond to the
       vertices of each quadrilateral region.  The ordering of the data in the file is such that  the  s  values
       are  changing  faster  than  the t values.  If a minus ('-') is given for dfile, then the values are read
       from the standard input.

       The third invocation form is used to read coordinate triplets from a file or  the  standard  input.   The
       three  dfile arguments must all be the same, and the corresponding file must contain three floating point
       values for each point location.  The ordering and other details are the same as  those  described  for  z
       value files above.

EXAMPLE

       To generate a tesselated sphere:

         gensurf crystal ball 'sin(PI*s)*cos(2*PI*t)' 'cos(PI*s)' 'sin(PI*s)*sin(2*PI*t)' 7 10

       To generate a 10x20 smoothed height field from 12 recorded vertex z values:

         gensurf dirt ground '10*s' '20*t' height.dat 2 3 -s

AUTHOR

       Greg Ward

BUGS

       The smoothing operation requires that functions be defined beyond the [0,1] boundaries of s and t.

SEE ALSO

       genrbox(1), genrev(1), genworm(1), icalc(1), obj2mesh(1), obj2rad(1), rpict(1), rvu(1), xform(1)

RADIANCE                                            11/15/93                                          GENSURF(1)