1. OBJ file
1. OBJ file overview
OBJ is a 3D model file, so it does not contain information such as animation, material properties, texture paths, dynamics, particles, etc.
OBJ files mainly support polygonal (Polygons) models. Although OBJ files also support Curves, Surfaces, and Point Group Materials, the OBJ files exported by Maya do not include these information.
OBJ files support surfaces with more than three points.
OBJ files support normals and texture coordinates.
2. OBJ file analysis
OBJ files do not require any kind of file header (File Header), although a few lines of file information are often used as the beginning of the file. The OBJ file is composed of lines of text, and the comment line starts with a "#" sign (#). Spaces and blank lines can be added to the file at will to increase the readability of the file.
Lines with words start with one or two marked letters, which are keywords (Keyword), which can indicate what kind of data this line is. Multiple lines can be logically joined together to represent one line by adding a hyphen (\) at the end of each line. Note that spaces or tabs cannot appear after the connector (\), otherwise it will cause file errors.
(1) Example
Below is the cube.obj data exported after creating the cube in maya:
# This file uses centimeters as units for non-parametric coordinates.
mtllib Cube.mtl
g default
v -0.500000 -0.500000 0.500000
v 0.500000 -0.500000 0.500000
v -0.500000 0.500000 0.500000
v 0.500000 0.500000 0.500000
v -0.500000 0.500000 -0.500000
v 0.500000 0.500000 -0.500000
v -0.500000 -0.500000 -0.500000
v 0.500000 -0.500000 -0.500000
vt 0.375000 0.000000
vt 0.625000 0.000000
vt 0.375000 0.250000
vt 0.625000 0.250000
vt 0.375000 0.500000
vt 0.625000 0.500000
vt 0.375000 0.750000
vt 0.625000 0.750000
vt 0.375000 1.000000
vt 0.625000 1.000000
vt 0.875000 0.000000
vt 0.875000 0.250000
vt 0.125000 0.000000
vt 0.125000 0.250000
vn 0.000000 0.000000 1.000000
vn 0.000000 0.000000 1.000000
vn 0.000000 0.000000 1.000000
vn 0.000000 0.000000 1.000000
vn 0.000000 1.000000 0.000000
vn 0.000000 1.000000 0.000000
vn 0.000000 1.000000 0.000000
vn 0.000000 1.000000 0.000000
vn 0.000000 0.000000 -1.000000
vn 0.000000 0.000000 -1.000000
vn 0.000000 0.000000 -1.000000
vn 0.000000 0.000000 -1.000000
vn 0.000000 -1.000000 0.000000
vn 0.000000 -1.000000 0.000000
vn 0.000000 -1.000000 0.000000
vn 0.000000 -1.000000 0.000000
vn 1.000000 0.000000 0.000000
vn 1.000000 0.000000 0.000000
vn 1.000000 0.000000 0.000000
vn 1.000000 0.000000 0.000000
vn -1.000000 0.000000 0.000000
vn -1.000000 0.000000 0.000000
vn -1.000000 0.000000 0.000000
vn -1.000000 0.000000 0.000000
s off
g pCube1
usemtl initialShadingGroup
f 1/1/1 2/2/2 4/4/3 3/3/4
f 3/3/5 4/4/6 6/6/7 5/5/8
f 5/5/9 6/6/10 8/8/11 7/7/12
f 7/7/13 8/8/14 2/10/15 1/9/16
f 2/2/17 8/11/18 6/12/19 4/4/20
f 7/13/21 1/1/22 3/3/23 5/14/24
(2) Keyword Description
# : comment marker
mtllib : describes the path where the material file (mtl) used by the model is located
v : vertex
vt : texture coordinates of the vertex
vn : the normal of the vertex
o : object name
g : group name
s : smoothing group (Smoothing group), which processes the lighting information between faces to achieve a smooth effect
usemtl : the currently used material
f : face
Among them, the surface f needs to be taken out, for example, f 7/13/21 1/1/22 3/3/23 5/14/24 means to draw a surface with four points, and the four sets of data separated by spaces represent the plane Four vertices, in each set of data, each number represents the index of the vertex / texture coordinate / normal , so f 7/13/21 1/1/22 3/3/23 5/14/24 The data for the first point (7/13/21) in is:
vertex |
texture coordinates |
normal |
（0.500000，-0.500000，-0.500000） |
（0.125000，0.250000） |
（-1.000000，0.000000，0.000000） |
Two, mtl file
1.mtl file overview
We know that .OBJ files are used to store model information. Observe the first line of code of cube.obj above, and you can see that the material library file is mtllib Cube.mtl
The .mtl file (Material Library File) is a material library file, which describes the material information of the object, stored in ASCII, and can be opened and edited by any text editor. A .mtl file can contain one or more material definitions, for each material there is a description of its color, texture and reflection map, applied to the surface and vertices of the object.
2.mtl file analysis
(1) Example
The cube.mtl file data is as follows:
newmtl initialShadingGroup
illum 4
Kd 0.50 0.50 0.50
Ka 0.00 0.00 0.00
Tf 1.00 1.00 1.00
Ni 1.00(2) Keyword Description
newmtl : represents the material, the following are the attribute parameters of the material
Ns : Specular reflection coefficient, the higher the value, the denser the highlight
NI : Specify the optical density of the material surface, that is, the refraction value
d : Indicates the number of objects blended into the background, the value range is 0.0~1.0, the value of 1.0 means completely opaque, and the value of 0.0 means completely transparent
Tr : defines the alpha transparency of the material
Tf : material transmission filter (transmission filter), the corresponding data is r, g, b value
illum : illumination (illumination), which can be followed by digital parameters in the range of 0~10
Ka: ambient light (ambient color)
Kd: scattered light (diffuse color)
Ks: specular light (specular color)
Ke : emissive color
map_Ka : The texture map path sampled by the ambient light, in the root directory of the .obj model file
map_Kd : texture map path sampled by diffuse light