Obj format Overview

We often see *. there are two types of obj files: the first is an OBJ File (also called the target File) in COFF (Common Object File Format) Format, which is used to compile applications; the second type is the OBJ model file launched by Alias | Wavefront. The OBJ file format I want to talk about is the second-OBJ model file. <BR> when talking about the 3D file format, you will not be unfamiliar with it ,"*. 3ds ","*. max ","*. lw ","*. mb ","*. dxf ","*. obj ", I believe everyone can list several. However, when talking about the specific features of the OBJ file, few people can give a more satisfactory description. Many people know that OBJ files start from using Poser. Poser is a human body modeling software that exports the human body generated by Poser to other 3D software for further processing, the OBJ file is used. OBJ files are a standard format of 3D model files and are suitable for intercommunication between 3D software models. For example, if you create a model in 3dsMax or LightWave and want to adjust it to rendering or animation in Maya, exporting the OBJ file is a good choice. Currently, almost all well-known 3D software supports reading and writing OBJ files. However, many software requires plug-ins to do this.
In addition, as an excellent file format, many game engines also support reading OBJ files. What is the usage of OBJ file format? If you do not learn programming, it is of little use. However, the interaction between 3D software models is a very common thing. Unfortunately, the current 3D software model export functions are not so perfect, there is often a lack of lines, and sometimes the exported model cannot be opened. If the situation is urgent, you will definitely study it at any cost and look forward to finding the cause and solving the problem. In this case, my tutorial may be of great help to you.
OBJ is a text file format, which means you can directly open it on the WordPad to view the changes. If you can understand what each line of content means, I believe it is not far from your successful solution.
OBJ file is a file format developed by Wavefront for its workstation-based 3D modeling and animation software "Advanced Visualizer.
The new version of OBJ is v3.0 instead of v2.11.
The OBJ3.0 format supports Polygon, Lines, Surfaces, and Free-form Curves ).
Straight Lines and polygons are described by their points, and curves and surfaces are defined based on their control points and additional information attached to the curve type. This information supports regular and irregular curves, including those based on the besserx curve, B-spline, Cardinal/Catmull-Rom spline ), and the curve of Taylor equations.
OBJ file-Features
(1) OBJ is a 3D model file. Therefore, it does not contain animation, material properties, texture paths, dynamics, particles, and other information.
(2) The OBJ file mainly supports Polygons models.
(3) The OBJ file supports three or more vertices.
(4) OBJ files support normal and texture coordinates.
The OBJ file does not support polygon with holes.
The OBJ file does not contain the color definition information, but can reference the material library. The material library information is stored in an independent file with the suffix ". mtl. The keyword "mtllib" indicates the meaning of the material library. The material library contains the diffuse, ambient, and specular definition values of materials. After "usemtl" specifies the material, the materials will be used in the future, the next "usemtl" is used to specify the new material.
OBJ file-Basic Structure
The OBJ file consists of a line of text. The comment line starts with a "well" (#). Spaces and blank lines can be added to the file at will to increase the readability of the file. A row with words starts with one or two marked letters, that is, the key word. A Keyword can indicate the data of a row. Multiple rows can be logically connected together to represent a row by adding a connector (\) at the end of each row (\).
Note that there cannot be spaces or tabs after the connector (\); otherwise, an error will occur in the file.
The following keywords can be used in the OBJ file.
In this list, keywords are arranged according to the data type. Each keyword has a brief description.
Vertex data ):
V Ric vertices)
Vt Texture coordinate point (Texture vertices)
Vn Vertex normal (Vertex normals)
Vp Parameter space vertex (Parameter space vertices)
Free-form curve/surface attributes ):
Deg (Degree)
Bmat base matrix)
Step size)
Cstype Curve or surface type (Curve or surface type)
Element (Elements ):
P Point (Point)
L Line)
F (Face)
Curv Curve (Curve)
Curv2 2D curve (2D curve)
Surf Surface)
Free-form curve/surface body statements ):
Parm Parameter value (Parameter values)
Trim external trim loop)
Inner trimming loop)
Scrv Special curve (Special curve)
Sp Special point)
End statement)
Connectivity between free form surfaces (between free-form surfaces ):
Con connection)
-Grouping ):
G Group name)
S smooth group)
Mg merge group)
O Object name)
-Display/render attributes ):
Bevel interpolation)
C_interp Color interpolation (Color interpolation)
D_interp Dissolve interpolation (Dissolve interpolation)
Level of detail)
Usemtl Material name (Material name)
Mtllib Material library (Material library)
Shadow_obj Shadow (Shadow casting)
Trace_obj Ray tracing)
Ctech Curve approximation Technology (Curve approximation technique)
Surface approximation technique)