SYNOPSIS

DESCRIPTION

EXAMPLE

AUTHOR

BUGS

SEE ALSO

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

**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** [

gensurf mat name dfile dfile dfile m n

*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.

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 |

Greg Ward

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

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