It also parses the full Wavefront NURBS file format, allowing trimmed NURBS
data to be imported from such programs as Rhino-3D; when
imported into PolyTrans or NuGraf, the NURBS data remains as true trimmed
NURBS, allowing the data to be exported as trimmed NURBS to such supported
file formats as Renderman RIB,
SoftImage or IGES. when outputting to a polygonal file format (Lightwave, MAX, etc.) the PolyTrans or NuGraf
export converter will tesselate the trimmed NURBS patches to optimized indexed polygon
lists prior to export.
This import converter is a complete and accurate implementation of
the Wavefront OBJ file format, including the parsing of all attributes in a Wavefront
material ('.mtl') file. The converter has been under constant and refined
development since 1992; it is one of the 'must have' import converters of
game developers and others requiring easy transport of indexed polygon data
or NURBS data amongst most of the 3D software programs currently on the
market. Many companies which sell 3D models
provide their datasets in the OBJ file format, so you can use
this converter to read in these data files and be guaranteed nice
rendered results.
The converter will also read material definitions from a
Wavefront material file (typically which has a file extension
'.mtl') if the material file is referenced within the Wavefront
geometry file (typically which has a file extension '.obj') using
the 'mtllib' keyword. If one or more Wavefront material files are
listed on a single line then all will be read into memory for
possible reference by the geometry file.
The converter first reads the entire file into memory; this
includes the vertex, normal and texture coordinate lists, their
indice lists, all group names, material names and texture names,
and the smoothing groups assigned to each polygon. Next, the
converter computes new vertex normals for polygons that don't
have any normals and that have a non-zero smoothing group
assigned to them. If no smoothing groups are found then the
converter optionally creates smoothed vertex normals based on the
angle between abutting polygon faces. As a last step, the
polygonal data is separated into separate objects based on a
user-chosen criteria.
A very useful feature of the OBJ importer is its ability to explode an imported mesh model, line model or pointset model based on their associated group name, object name, smoothing group number, material name or texture map name. This is one of the most complex aspects of the Wavefront OBJ importer.
NOTES
If any texture map names are found in the .obj file ('usemap
', which is the old-style Wavefront texture reference
method) and the 'Use Material Name' drop-down list box option is
enabled then texture definitions will be automatically created
for these texture names and will be assigned to their
corresponding surfaces. NOTE:: you can distinguish these textured
surfaces because the texture map name is appended to the end of
the surface name (the surface and texture names are separated by
three underscores '_').
All texture map information is read in from a material file.
The supported mapping parameters include:map_Ka, map_Kd, map_Ks,
map_d, map_refl and map_bump. All sub-option parameters are also
read into memory and mapped to equivalent internal database
values: -o, -s, -mm and -bm.
If one or more group names are found on a 'g' line, then
they are appended all together to form the group name used
internally (ie: 'g all airplane tail_fin').
Dialog Box Options
The following information explains the various options on the
dialog box:
Import Meshes
If this checkbox is enabled then polygonal meshes will be imported. Meshes are defined by lines in the OBJ file which begin with the letter "f" or "fo".
Import Lines
If this checkbox is enabled then 3D lines will be imported. Lines are defined by lines in the OBJ file which begin with the letter "l".
Import Point Sets
If this checkbox is enabled then 3D point sets will be imported. Point sets are defined by lines in the OBJ file which begin with the letter "p".
Remove redundant vertices, normals and texture coordinates
If this checkbox is enabled then redundant vertices, normals and texture coordinates are removed from meshes, lines and point sets. This is the default.
Compute normals using assigned smoothing groups
If this checkbox is enabled then new vertex normals will be
computed for a polygon if it does not have any vertex normals
already and it has been assigned a non-zero smoothing group
number. Two abutting polygons will appear to be smooth only if
they share common vertices.
Compute averaged normals
If this checkbox is enabled then new vertex normals will be
computed for a polygon if it does not have any vertex normals
already, and it does not have a smoothing group assigned to it or
the 'Compute normals using assigned smoothing groups' checkbox is
disabled. The smoothing criterion is based on the angle between
abutting polygons; common smoothed vertex normals will be
computed if the angle between their geometric surfaces normals is
less than the angle specified on the dialog box (which defaults
to 30 degrees).
Make imported material names unique
If this checkbox is enabled (which is the default) then the
import converter will make all new material names unique if there
are conflicts upon import. For example, if a model currently
resides in memory which uses a surface definition (a 'material')
named 'redbricks' and another Wavefront file is read into memory
which also contains the material called 'redbricks' then this
second reference will be renamed to 'redbricks#2' once it has
been imported into the scene. The benefit of enabling this option
is that two imported files will use completely different
material/surface definitions, even if the imported files are read
in from the same Wavefront .obj file.
If this checkbox is disabled then any imported file which
makes references to materials that are already loaded into the
scene will use those materials/surfaces rather than create new
unique ones. Disabling this option is useful if multiple
Wavefront .obj files share a common Wavefront .mtl file (ie: all
imported .obj files should only share one set of material/surface
definitions in memory).
This Wavefront import converter has the unique feature of being able to import complete trimmed NURBS model descriptions from a Wavefront OBJ file. If this checkbox is enabled (check-marked) then trimmed NURBS models will be imported. If disabled (un-checkmarked) then all NURBS models will be ignored.
If you wish to prevent the trim curves of each NURBS patch from being imported then disable the "Import trim curves for NURBS patches" checkbox.
Read Wavefront.mtl material files
If this checkbox is enabled then the import converter will read
in and parse any Wavefront .mtl material files referenced within
the .obj file (via the keyword 'usemtl'). If this option is
disabled then no material files will be read.
Read texture information from .mtl material files
If this checkbox is enabled then the texture mapping information
found in a Wavefront .mtl material file will be read into memory
and stored along with the new surface definitions created. If
this checkbox is disabled then no texture mapping information
will be read in from the material file.
Color scaling: Ambient, diffuse, specular
These three values allow the intensity of the ambient ('Ka'),
diffuse ('Kd') and specular ('Ks') colors found within a
Wavefront .mtl material file to be scaled brighter or darker.
Many 3d programs export Wavefront material colors overly
saturated (ie: ambient = 100% white, diffuse = 100% white)
whereas many 3d rendering programs would like to see these values
at about 30% to 50% of full saturation. For example, if the 'Ka'
value is set to 0.3 and the ambient material color is specified
as (1 1 1) = 100% white, then the ambient color will be read into
the database as (0.3, 0.3, 0.3) = 30% white.
Report statistics about the geometry file
If this checkbox is enabled then statistics about the geometry
file will be reported once it has been read in and processed.
Print warning messages
If this checkbox is enabled then warning messages will be
reported as the file is read in. Warnings include unrecognized
input and options, out-of-range texture coordinates and out-of-
range index values.
Source for the Surface Name
This drop-down list box specifies which method the converter is
to use to assign a surface definition to each polygon. Automatic
assignment of surfaces to the polygons will save you a lot of
time and headache.
Use material name, else group names if no materials
found
The surface name will be taken from the material name assigned to
each polygon. If no materials are found in the file then the
surface name will be taken from the group name assigned to each
polygon. ace name will be taken from the material name assigned
to each polygon. If no group names are assigned to the polygons
then the surface name will be taken from the object name assigned
to each polygon. If no material, group or object name is assigned
then the "default" surface will be used.
This is the default method.
Use material names found in file, else "default" surface if
no materials
This will use the material name associated with each polygon as
the surface name. If no material name is assigned then the
"default" surface will be used.
Use group names found in file, else "default" surface if no
groups
This will use the group name associated with each polygon as the
surface name. If no group name is assigned then the "default"
surface will be used.
Use object names found in file, else "default" surface if
no objects
This will use the object name associated with each polygon as the
surface name. If no object name is assigned then the "default"
surface will be used.
Method for Splitting Polygons into Different Objects.
If your 3D scene is going to have many different objects in it
then it is recommended that the OBJ not be split up. However, if
you want to modify each individual part in the OBJ file then you
will want to split it up into different objects.
Don't split into different objects
This option prevents the OBJ file from being split up into
separate objects.
Split by object name
This will split the polygonal geometry according to the object
name assigned to each polygon.
Objects are assigned to polygons in the OBJ file by preceding
them with a line like: 'o ... '.
Split by group name
This will split the polygonal geometry according to the group
name assigned to each polygon. It is the most logical method for
splitting the geometry since the group names are usually assigned
on an object-name basis by the person who designed the 3D model.
Groups are assigned to polygons in the OBJ file by preceding
them with a line like: 'g ... '.
Split by material name
This will split the polygonal geometry according to the material
name assigned to each polygon. You may want to use this method if
no group names are provided in the file or if it makes more sense
to split by material name than by group name (for example, the
object might have 300 odd group names but 20 carefully chosen
material names).
Materials are assigned to polygons in the OBJ file by
preceding them with a line like: 'usemtl '.
Split by texture map name
This will split the polygonal geometry according to the texture
map name assigned to each polygon. In most cases you will not use
this method.
Texture map names are assigned to polygons in the OBJ file by
preceding them with a line like: 'usemap '.
Split by smoothing group numbers
This will split the polygonal geometry according to the smoothing
group number assigned to each polygon. Since smoothed polygons
are usually clustered together as one sub-object this method can
be used to accurately extract sub-objects from the polygonal
data. However, it will probably create many more new objects than
would the 'Split by group name' method above.
Smoothing groups are assigned to polygons in the OBJ file by
preceding them with a line like: 's '.
NOTES