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.\" RCSid "$Id: obj2mesh.1,v 1.11 2008/11/10 19:08:17 greg Exp $"
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.TH OBJ2MESH 1 03/11/03 RADIANCE
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.SH NAME
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obj2mesh - create a compiled RADIANCE mesh file from Wavefront .OBJ input
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.SH SYNOPSIS
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.B obj2mesh
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[
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.B "\-a matfile"
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][
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.B "\-l matlib"
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][
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.B "\-n objlim"
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][
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.B "\-r maxres"
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][
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.B \-w
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]
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[
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.B "input.obj"
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[
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.B "output.rtm"
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]
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]
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.SH DESCRIPTION
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.I Obj2mesh
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reads a Wavefront .OBJ file from
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.I input.obj
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(or the standard input) and compiles it into a RADIANCE triangle mesh,
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which is sent to
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.I output.rtm
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(or standard output).
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Any RADIANCE material descriptions included via one or more
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.I \-a
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options will be compiled and stored in the mesh as well.
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If the
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.I \-l
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option is used to specify a material file, the RADIANCE library
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locations are searched.
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This mesh may be included in a RADIANCE scene description via the
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.I mesh
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primitive, thus:
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.IP "" .2i
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mod mesh id
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.br
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1+ output.rtm [xform args]
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.br
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0
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.br
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0
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.PP
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The syntax and semantics are identical to the RADIANCE
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.I instance
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primitive.
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If
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.I mod
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is "void", then the stored mesh materials will be applied during rendering.
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Otherwise, the given material will be substituted on
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all the mesh surfaces.
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.PP
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The
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.I \-n
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option specifies the maximum surface set size for
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each voxel.
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Larger numbers result in quicker mesh generation,
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but potentially slower rendering.
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Values below 6 are not recommended, since this is the median
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valence for a mesh vertex (the number of adjacent faces),
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and smaller values will result in pointless octree subdivision.
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The default setting is 9.
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.PP
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The
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.I \-r
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option specifies the maximum octree resolution.
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This should be greater than or equal to the ratio of the mesh bounding
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box to the smallest triangle.
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The default is 16384.
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.PP
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The
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.I \-w
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option suppresses warnings.
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.PP
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Although the mesh file format is binary, it is meant to be portable
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between machines.
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The only limitation is that machines with radically different integer
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sizes will not work together.
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.SH DETAILS
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The following Wavefront statements are understood and compiled by
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.I obj2mesh.
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.TP 10n
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.BI v " x y z"
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A vertex location, given by its Cartesian coordinates.
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The final mesh position may of course be modified by
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the transform arguments given to the
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.I mesh
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primitive in the Radiance scene description.
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.TP
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.BI vn " dx dy dz"
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A vertex normal vector, given by its three
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direction components, which will be normalized by
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.I obj2mesh.
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Normals will be interpolated over the mesh
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during rendering to produce a smooth surface.
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If no vertex normals are present, the mesh will appear tesselated.
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A zero length normal (i.e., 0 0 0) will generate a syntax error.
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.TP
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.BI vt " u v"
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A local vertex texture coordinate.
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These coordinates will be interpolated and passed
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to the "Lu" and "Lv" variables during rendering.
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Local coordinates can extend over any desired range of values.
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.TP
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.BI usemtl " mname"
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A material name.
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The following faces will use the named material, which is
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taken from the material definitions in the
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.I \-a
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input file(s).
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.TP
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.BI g " gname"
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Group association.
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The following faces are associated with the named group.
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If no "usemtl" statement has been
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encountered, the current group is used for the surface material
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identifier.
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.TP
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.BI f " v1/t1/n1 v2/t2/n2 v3/t3/n3" " .."
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A polygonal face.
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Polygon vertices are specified as three indices separated
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by slashes ('/').
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The first index is the vertex location, the
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second index is the local (u,v) texture coordinate, and the
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third index is the vertex surface normal.
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Positive indices count from the beginning of the input,
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where the first vertex position (
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.I v
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statement) is numbered 1, and likewise
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for the first texture coordinate and the first surface normal.
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Negative indices count backward from the current position in
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the input, where \-1 is the last vertex encountered, \-2
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is the one before that, etc.
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An index of 0 may be used for the vertex texture or normal to
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indicate none, or these may be left off entirely.
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All faces will be broken into triangles in the final mesh.
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.PP
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All other statement types will be ignored on the input.
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Statements understood by
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.I obj2rad(1)
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will be ignored silently; other statements will generate
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a warning message after translation to indicate how much was missed.
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.SH DIAGNOSTICS
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There are four basic error types reported by obj2mesh:
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.IP
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warning - a non-fatal input-related error
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.IP
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fatal - an unrecoverable input-related error
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.IP
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system - a system-related error
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.IP
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internal - a fatal error related to program limitations
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.IP
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consistency - a program-caused error
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.PP
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Most errors are self-explanatory.
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However, the following internal errors should be mentioned:
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.IP "Set overflow in addobject (id)"
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This error occurs when too many surfaces are close together in a
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scene.
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Sometimes a dense mesh can be accommodated by increasing
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the maximum resolution (by powers of two) using the
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.I \-r
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option, but usually this error indicates something is wrong.
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Either too many surfaces are lying right on top of each other,
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or the bounding cube is inflated from disparate geometry
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in the input.
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Chances are, the face number "id" is near
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those causing the problem.
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.IP "Hash table overflow in fullnode"
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This error is caused by too many surfaces, and there is
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little hope of compiling this mesh.
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.SH EXAMPLES
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To create a compiled triangle mesh from the scene file mesh.obj
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using materials from the file mesh.mat:
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.IP "" .2i
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obj2mesh \-a mesh.mat mesh.obj mesh.rtm
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.PP
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To use local coordinates to place a square tiled image on a mesh object:
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.sp
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.nf
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void colorpict tiled_pat
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7 red green blue mytile.hdr . frac(Lu) frac(Lv)
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0
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0
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tiled_pat plastic tiled_mat
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0
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0
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5 .9 .9 .9 0 0
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tiled_mat mesh tiled_mesh
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1 mymesh.rtm
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0
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0
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.fi
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.SH ENVIRONMENT
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RAYPATH the directories to search for material files.
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.SH AUTHOR
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Greg Ward
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.SH "SEE ALSO"
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gensurf(1), getinfo(1), make(1), obj2rad(1),
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oconv(1), rpict(1), rvu(1), rtrace(1), xform(1)
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