OBJ Converter

Table of Contents

• Overview
• Scope
• Mapping
  • Import Mapping
    • Product Structure
  • Export Mapping
    • Product Structure
• Parameters
  • Importer Parameters
  • Exporter Parameters

Overview

OBJ_Reader can read files and OBJ_Writer can write files in Wavefront OBJ file format.

The reader can read files with external .mtl (material library) files, files with both multiple and single parts. In the case of multiple parts they are created as roots of the resulting model (ModelData_Model).

Scope

Import	Export
polygonal representations colors, materials, textures	polygonal representations colors, materials, textures

Mapping

Import Mapping

Below table shows how OBJ content are mapped into CAD Exchanger entities after import.

Product Structure

OBJ tag	Description	CAD Exchanger Entity	Note
v	vertex data	ModelData_Part	All accumulated data between "g" tags maps directly to ModelData_IndexedTriangleSet.
vn	vertex normals data
vt	texture coordinates data
f	face data
o	object name
g	group name
matlib	external .mtl file name
usemlt	specifies the material name for the element following it

Export Mapping

Below table shows how CAD Exchanger entities are mapped into OBJ entities after export. Note that OBJ could not store the hierarchy therefore all polygonal data of every instance of part will be bake in the world coordinate system.

Product Structure

CAD Exchanger Entity	OBJ tag	Note
ModelData_Assembly	v / vn / vt / f / g / o / matlib / usemlt
ModelData_Part		Every body of part will map to OBJ-group (surrounded with "g" tag)
ModelData_Instance

Parameters

Importer Parameters

The OBJ import parameters are controlled by OBJ_ReaderParameters. The following table contains a list of parameters for OBJ import:

Parameter	Default value	Description
SetLengthUnit (Base_LengthUnit LengthUnit)	Base_LU_Millimeters	See Base_ReaderParameters::SetLengthUnit(Base_LengthUnit LengthUnit).

Exporter Parameters

The OBJ export parameters are controlled by OBJ_WriterParameters. The following table contains a list of parameters for OBJ export:

Parameter	Default value	Description
ToGenerateMtlFile()	true	Specifies whether a separate .mtl file (with material library) should be created. If the value is true then an .mtl file is created. The .mtl file will have the same base file name as the resulting .obj file. If the value is false then no colors will be stored and no .mtl file will be created.
WriteNormals()	true	Specifies whether vertex normals should be saved in a resulting .obj file. If the value is true then normals are stored in the file. In this case, third-party viewers may display 3D models in smooth shading. If the value is false then normals are not stored in the .obj file, and the third-party viewers may display 3D models in flat shading.
OverrideDuplicateNames()	true	Specifies whether original names of parts should be supplemented with suffixes. If the value is true the name of every part encountered twice or more during export will be supplemented with a suffix to make the name unique. This is done to avoid merging of geometries with same name during import by receiving CAD applications. If the value is false every part will be exported with its original name. This may cause geometric objects with the same name to be merged by receiving CAD applications into one geometric object.
ReplaceSpacesInNames()	false	Specifies whether original names should be overridden by names without space characters. If the value is true then the space characters in parts' names will replaced by "_" characters for better compatibility with receiving systems. If the value is false every part will be exported with its original name.
LengthUnit()	Base_LU_Millimeters	See Base_WriterParameters::LengthUnit().