Obj file format and.Mtl file format

1.OBJ It's a kind of 3D Model file , therefore No animation 、 Material properties 、 Map path 、 Dynamics 、 The particle Etc . But you can read .mtl file To get material information .

2.OBJ Files use 【 Keywords are arranged according to data type , Each keyword has a short description 】
　    Vertex data (Vertex data)：
　　v  Geometry vertices (Geometric vertices)
　　vt Map coordinate points (Texture vertices)
　　vn Vertex normals (Vertex normals)
　　vp Parameter space vertex (Parameter space vertices)

3. stay Maya Create a polygon cube , Select this cube , The export format is OBJ, The file named "cube.obj".（ If there is no such format , Please be there. Plug-in Manager In the load "objExport.mll") Open with a tablet "cube.obj". For example, below ：

usemtl initialShadingGroup

v 0.500000 -0.500000 -0.500000
vt 1.000000 0.000000

vn 0.000000 0.000000 -1.000000

s off

f  1 2 3

f  1/3 2/5 3/4

f  1/3/4 2/5/6 3/4/2
 

Explain it. ：

       "v 0.500000 -0.500000 -0.500000" This sentence "v" Represents the coordinates of the point .
　　"vt 1.000000 0.000000" This sentence "vt" Mapping coordinates representing points .
　　"vn 0.000000 0.000000 -1.000000" This sentence "vn" Represents the normal of the point .
　　"s off" Indicates that the smoothing group is turned off .
　　"usemtl initialShadingGroup" Indicates the material used .
　　"f  1 2 3" Such lines are represented by 1、2、3 The vertex of No. 2 forms a triangle .
       "f  1/3 2/5 3/4" Such lines are represented by 1、2、3 The vertex of No. 2 forms a triangle , The index value of the texture coordinate of the first vertex is 3, The index value of the texture coordinate of the second vertex is 5, The index value of the texture coordinate of the third vertex is 4.
       "f  1/3/4 2/5/6 3/4/2" Such lines are represented by 1、2、3 The vertex of No. 2 forms a triangle , The index value of the texture coordinate of the first vertex is 3, The index value of its normal is 4; The index value of the texture coordinate of the second vertex is 5, The index value of its normal is 6; The index value of the texture coordinate of the third vertex is 6, The index value of its normal is 2.

4. say something .mtl file Well

     3D model processing will read .mtl File to get material information .

    mtl file （Material Library File） Is a material library file , It describes the material information of the object ,ASCII Storage , Any text editor can open and edit it . One .mtl The file can contain one or more material definitions , Each material has its own color , Description of texture and reflection map , Applied to surfaces and vertices of objects .
The following is the basic structure of a material library file ：
newmtl mymtl_1
    Material color lighting definition
    Texture map definition
    Reflection map definition
newmtl mymtl_2
    Material color lighting definition
    Texture map definition
    Reflection map definition
notes ： Each material library can contain multiple material definitions , Each material has a material name . use newmtl mtlName To define a material . For each material , Its color, illumination, texture, reflection and other descriptive features can be defined .
The main definition format is shown below ：
Material color illumination
1. Environmental reflection has the following three description formats , The three are mutually exclusive , Can't be used at the same time .

Ka r g b    \\ use RGB Color value to represent ,g and b Two parameters are optional , If only r Value , be g and b All the values of are equal to r Value . The general value range of the three parameters is 0.0~1.0, Values outside this range increase or decrease reflectivity accordingly ;
Ka spectral file.rfl factor   \\ Use one rfl Documents to show .factor Is an optional parameter , Express .rfl Multiplier of the value in the file , The default is 1.0;
Ka xyz x y z   \\ use CIEXYZ Value to represent the ,x,y,z yes CIEXYZ Component values of color space .y and z Two parameters are optional , If only x Value , be y and z All the values of are equal to r Value . The general value range of the three parameters is 0~1.

2. Three formats of diffuse description ：
Kd r g b
Kd spectral file.rfl factor
Kd xyz x y z

3. Three formats of mirror reflection description :
Ks r g b
Ks spectral file.rfl factor
Ks xyz x y z

4. Three formats of filter transmittance description ：
Tf r g b
Tf spectral file.rfl factor
Tf xyz x y z

5. Lighting model description format ：

illum illum_#
Specify the lighting model of the material .illum It can be followed by 0~10 Numerical parameters in the range .
 

5. download 3D The website of the model ：https://free3d.com/

6. more , Please refer to

obj File parsing - giser_xupf - Blog Garden

OBJ Model files and MTL Material file Introduce _ Changjiang many blogs -CSDN Blog _mtl texture of material