NAME
tmesh2rad - convert a triangular mesh to a RADIANCE scene description
SYNOPSIS
tmesh2rad [ -o obj ][ -m mat ][ -p pat ] [ input .. ]
DESCRIPTION
Tmesh2rad converts one or more triangle-mesh files to a RADIANCE scene
description. The -o option may be used to assign a default object
name. The single letter "T" is used if no name is given on the command
line or in the file. The -m option may be used to assign a default
material name. The non-material "void" is used as a default if none is
given on the command line or in the file. The -p option may be used to
assign a default picture for a surface pattern. If none is given on
the command line or in the file, the surface will not have an
associated pattern.
FILE FORMAT
A triangle-mesh is a free-format ASCII file composed of the following
eight primitive types. Each primitive is begun with a single, white-
space-delimited letter:
# Comment Whatever follows up until the end of line is passed as a
comment to the output. Note that there must be at least one
space or tab following the pound-sign.
o name The white-space-delimited string name is used as a prefix for
all following output triangles.
m material
The white-space-delimited string material is used as the
modifier name for all following output triangles.
p picture The white-space-delimited string picture is used as the name
of the RADIANCE picture file to be used as a pattern for all
following output triangles with properly defined vertices.
(See i primitive below.)
v id x y z
Defines the vertex id with 3-dimensional coordinates x, y and
z. The identifier, id must be some small, non-negative
integer value. If the same integer is used for a later
vertex definition, this definition will be lost, though any
triangles using the vertex prior to its redefinition will be
unaffected.
n nx ny nz
Defines a surface normal vector with the 3-dimensional
components nx, ny and nz. This vector will be associated
with the most recently defined vertex, and is often placed on
the same line as the vertex definition for clarity. The
vector need not be normalized.
i u v Defines a picture index for the most recently defined vertex.
The u value will be used to lookup the horizontal pixel
coordinate in the currently defined picture. The v value
will be used to lookup the vertical pixel coordinate. (See
the RADIANCE reference manual for details on picture
coordinate values.) As with associated surface normals,
picture indices are interpolated using barycentric
coordinates based on the triangle vertices. If these
coordinates are calculated correctly, this should result in a
smooth mapping of a pattern onto the surface mesh.
t id1 id2 id3
Create a triangle connecting the three vertices identified by
id1, id2 and id3. The right-hand rule is used to determine
the default surface normal orientation, and this should not
be too far from the associated vertex normals (if any). All
three vertices must have an associated normal if the triangle
is to be smoothed. If a picture file is defined and all
three vertices have pattern indices associated with them,
then this picture will be used as a pattern to modify the
triangle’s color.
We realize there are many similar T-mesh file formats in existence, and
that it would have been just as easy to support one of these formats
directly. The disadvantage to supporting an existing format is that
conversion from other formats might prove difficult. It was our hope
to provide a "greatest common multiple" format that would support all
similar T-mesh formats, rather than supporting WaveFront’s .obj format
(for example) and being unable to associate a pattern with an object.
Converting from other formats should be relatively straightforward. In
many cases, an awk(1), rcalc(1) or even a sed(1) script should be
sufficient.
EXAMPLE
Here is an example T-mesh file:
# Our object name:
o test_object
# Our material:
m puce
# Our vertices:
v 1 10 15 5
v 2 10 -15 5
v 3 0 -15 0
v 4 -10 15 -5
# Two triangles joined together:
t 1 2 3
t 2 3 4
Which generates the following output:
## T-mesh read from: <stdin>
# Our material:
# Our vertices:
# Two triangles joined together:
puce polygon test_object.1
0
0
9
10 15 5
10 -15 5
0 -15 0
puce polygon test_object.2
0
0
9
10 -15 5
0 -15 0
-10 15 -5
Here is another example:
# A partial cylinder:
m BluePlastic
v 1 -14.673 -3.119 50 n -0.95677 -0.203374 1.17936e-10
v 2 -12.136 -8.817 -50 n -0.791363 -0.574922 4.84915e-10
v 3 -12.136 -8.817 50 n -0.791363 -0.574922 4.84915e-10
t 1 2 3
m OrangePlastic
v 1 -7.501 -12.991 50 n -0.549094 -0.812427 -1.45812e-09
v 2 -12.136 -8.817 50 n -0.791363 -0.574922 4.84915e-10
v 3 -12.136 -8.817 -50 n -0.791363 -0.574922 4.84915e-10
t 1 2 3
m BluePlastic
v 1 -1.568 -14.918 50 n -0.171094 -0.965568 -5.69788e-09
v 2 -7.501 -12.991 50 n -0.549094 -0.812427 -1.45812e-09
v 3 -7.501 -12.991 -50 n -0.429001 -0.881759 -3.6502e-09
t 1 2 3
Note that the same three vertices were used repeatedly, and
intermingled with the triangle definitions.
AUTHOR
Greg Ward
BUGS
Triangle smoothing doesn’t work very well for glass or trans material
types in Radiance, since textures cause distorted transmission through
these materials. It is best to use the dielectric material type if
smooth transmission is desired.
SEE ALSO
arch2rad(1), awk(1), ies2rad(1), thf2rad(1), oconv(1), rcalc(1),
sed(1), xform(1)