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.\" RCSid "$Id: obj2rad.1,v 1.4 2007/09/04 17:36:40 greg Exp $" |
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.TH OBJ2RAD 1 6/14/94 RADIANCE |
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.SH NAME |
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obj2rad - convert Wavefront .OBJ file to RADIANCE description |
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.SH SYNOPSIS |
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.B obj2rad |
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[ |
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.B \-n |
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][ |
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.B \-f |
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][ |
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.B "\-m mapfile" |
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][ |
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.B "\-o objname" |
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] |
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[ |
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.B input |
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] |
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.SH DESCRIPTION |
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.I Obj2rad |
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converts a Wavefront .OBJ file to a RADIANCE scene description. |
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The material names for the surfaces will assigned based on the |
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mapping rules file given in the |
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.I \-m |
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option. |
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If no mapping file is given, the identifiers given by the "usemtl" |
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statements will be used as the material names. |
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If no "usemtl" statements are found, the group names (given by |
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the "g" statement) will be used instead. |
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Failing this, the default material "white" will be used. |
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.PP |
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A mapping file contains a list of materials followed by the conditions |
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a surface must satisfy in order to have that material. |
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For example, if we wanted all faces in the Group "thingy" with |
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texture Map "pine" to use the material "wood", |
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and all other surfaces to use the |
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material "default", we would create the following mapping file: |
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.nf |
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|
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default ; |
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wood (Group "thingy") (Map "pine") ; |
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|
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.fi |
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All faces would satisfy the first set of conditions (which is empty), |
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but only the faces in the Group "thingy" |
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with texture Map "pine" would satisfy the |
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second set of conditions. |
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.PP |
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Each rule can have up to one condition per qualifier, and different |
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translators use different qualifiers. |
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In |
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.I obj2rad, |
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the valid qualifiers are |
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.I "Material, Map, Group, Object" |
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and |
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.I Face. |
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A condition is either a single value for a |
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specific attribute, or an integer range of values. |
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(Integer ranges are |
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specified in brackets and separated by a colon, eg. [\-15:27], and are |
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always inclusive.) A semicolon is used to indicate the end of a rule, |
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which can extend over several lines if necessary. |
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.PP |
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The semantics of the rule are such that "and" is the implied conjunction |
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between conditions. |
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Thus, it makes no sense to have more than one |
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condition in a rule for a given qualifier. |
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If the user wants the same |
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material to be used for surfaces that satisfy different conditions, |
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they simply add more rules. |
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For example, if the user also wanted faces between 50 and 175 in the |
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Group "yohey" to use "wood", |
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they would add the following rule to the end of the example above: |
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.nf |
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|
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wood (Face [50:175]) (Group "yohey") ; |
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|
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.fi |
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Note that the order of conditions in a rule is irrelevant. |
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However, |
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the order of rules is very important, since the last rule satisfied |
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determines which material a surface is assigned. |
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.PP |
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By convention, the identifier "void" is used to delete unwanted |
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surfaces. |
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A surface is also deleted if it fails to match any rule. |
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Void is used in a rule as any other material, but it has the |
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effect of excluding all matching surfaces from the translator output. |
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For example, the following mapping would delete all surfaces in the |
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Object "junk" except those with the Group name "beige", to which it |
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would assign the material "beige_cloth", and all other surfaces |
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would be "tacky": |
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.nf |
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|
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tacky ; |
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void (Object "junk") ; |
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beige_cloth (Object "junk") (Group "beige") ; |
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|
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.fi |
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.PP |
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The |
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.I \-n |
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option may be used to produce a list of qualifiers from which to construct |
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a mapping for the given .OBJ file. |
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This is also useful for determining which materials must be defined |
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when no mapping is used. |
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.PP |
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The |
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.I \-f |
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option is used to flatten all faces, effectively ignoring vertex |
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normal information. |
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This is sometimes desirable when a smaller model or more robust |
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rendering is desired, since interpolating vertex normals takes time |
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and is not always reliable. |
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.PP |
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The |
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.I \-o |
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option may be used to specify the name of this object, though it |
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will be overriden by any "o" statements in the input file. |
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If this option is absent, and there are no "o" statements, |
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.I obj2rad |
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will attempt to name surfaces based on their group associations. |
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.PP |
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If no input files are given, the standard input is read. |
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.SH DETAILS |
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The following Wavefront statements are understood and translated by |
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.I obj2rad. |
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.TP 10n |
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.BR # |
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A comment. |
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This statement is passed to the output verbatim. |
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It has no effect. |
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.TP |
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.BR f |
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A polygonal face. |
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If the vertices have associated surface normals, the face |
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will be broken into quadrilaterals and triangles with the |
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appropriate Radiance textures to interpolate them. |
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Likewise, if the face is non-planar, it will be broken |
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into triangles. |
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Each face in the input file is assigned a number, starting with 1, |
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and this number may be used in the material mapping rules. |
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.TP |
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.BR g |
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Group association. |
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The following faces are associated with the named group(s). |
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These may be used in the mapping rules, where a rule is matched |
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if there is an association with the named Group. |
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(I.e. since there may be multiple group associations, any match |
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is considered valid.) |
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If a mapping file is not used and no "usemtl" statement has been |
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encountered, the main group is used for the surface material |
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identifier. |
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.TP |
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.BR o |
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Object name. |
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This is used to name the following faces, and may be used |
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in the mapping rules. |
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.TP |
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.BR usemap |
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A texture map (i.e. Radiance pattern) name. |
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The name may be used in the material mapping rules, but |
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the indexing of Radiance patterns is not yet supported. |
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.TP |
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.BR usemtl |
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A material name. |
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The name may be used in mapping rules, or will be used |
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as the Radiance material identifier if no mapping is given. |
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.TP |
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.BR v |
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A vertex, given by its x, y and z coordinates. |
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.TP |
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.BR vn |
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A vertex normal, given by its x, y and z direction components. |
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This vector will be normalized by |
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.I obj2rad, |
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and an error will result if it has length zero. |
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.TP |
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.BR vt |
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A vertex texture coordinate. |
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Not currently used, but will be if we ever get around to |
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supporting Wavefront textures. |
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.PP |
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All other statement types will be ignored on the input. |
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A final comment at the end of the Radiance output file will give some |
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indication of how successful the translation was, since |
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it will mention the number of statements |
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.I obj2rad |
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did not recognize. |
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.SH EXAMPLES |
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To create a qualifier list for triceratops.obj: |
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.IP "" .2i |
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obj2rad \-n triceratops.obj > triceratops.qual |
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.PP |
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To translate triceratops.obj into a RADIANCE file using the mapping |
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triceratops.map: |
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.IP "" .2i |
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obj2rad \-m triceratops.map triceratops.obj > triceratops.rad |
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.SH FILES |
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tmesh.cal - used for triangle normal interpolation |
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.br |
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surf.cal - used for quadrilateral normal interpolation |
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.SH AUTHOR |
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Greg Ward |
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.SH "SEE ALSO" |
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arch2rad(1), ies2rad(1), obj2mesh(1), objutil(1) oconv(1), thf2rad(1), xform(1) |
