Wavefront Obj File and Texture Mapping

[Riigel]

Hey everyone,

i need some information about obj files. I was able to extract a model with textures from a game file. The extracted file looks like this.

Code: Select all

g Mesh 0
v 0.053712 0.020744 -0.039279
v 0.061784 0.008303 -0.013566
v 0.053478 0.007107 -0.034874
v 0.024713 0.154537 0.04836
vt 0.175401 0.654691
vt 0.169565 0.67048
vt 0.175952 0.67048
vt 0.107216 0.547805
f 4 1 3
f 2 3 1

Now my Questions:
1. The vertex texture command defines how a texture is mapped on the object, right?
2. The face command defines the triangles from the object. What about the vt command, must they have a face definition?
3. How can i include the texture in the obj file? I wanna open the obj
(Blender, Max,..) and see the complete textured object.
4. Are more information necessary for mapping a texture to a object?

[porimac]

Hi,Riigel.

1. The vertex texture command defines how a texture is mapped on the object, right?

Right. vt = Texture vertices uv.

2. The face command defines the triangles from the object. What about the vt command, must they have a face definition?

vt command are not the meanings about meshs. they meaning Vertices.

3. How can i include the texture in the obj file? I wanna open the obj
(Blender, Max,..) and see the complete textured object.

you will make MTL file.
and write mtllib/usemtl command in obj file.

4. Are more information necessary for mapping a texture to a object?

I recommend you to examine OBJ/MTL fileformat.
http://www.cs.clemson.edu/~dhouse/cours ... ormat.html
http://www.fileformat.info/format/material/

however, I am noob and Jap talker, I might be wrong. :p

[Riigel]

I have read about the mdl file but it doesn't work for me.
Maybe someone can help me.

I think my example must look like:

Code: Select all

mtllib mat.mtl
g Mesh 0
v 0.053712 0.020744 -0.039279
v 0.061784 0.008303 -0.013566
v 0.053478 0.007107 -0.034874
v 0.024713 0.154537 0.04836
vt 0.175401 0.654691
vt 0.169565 0.67048
vt 0.175952 0.67048
vt 0.107216 0.547805
usemtl tex
f 4 1 3
f 2 3 1

But what is about the mtl file. The object has only one texture in dds format (no Reflection Map, Ambient Occlusion or Normal map).

1. Do i need the the Ka, Kd, Ks statements for a single textured object?
2. If yes, how i get the values for Ka,Kd,Ks? Must they stored in the model file?
3. Can i use dds format for textures?

Code: Select all

newmtl tex
Ka 0.0435 0.0435 0.0435
Kd  0.5922  0.0166  0.0000
Ks  0.5974  0.2084  0.2084
map_Ka tex.dds

[finale00]

http://en.wikipedia.org/wiki/Wavefront_.obj_file

Most of your questions are answered there.
IMO, it is summarized nicely and orderly.

It is an overview of the full specs, which is also available in an external link.

2. The face command defines the triangles from the object. What about the vt command, must they have a face definition?

There are 4 different face definitions.

1: f v1 v2 v3 - just coords
2: f v1/vn1 v2/vn2 v3/vn3 - coords + normals
3: f v1/vn1/vt1 v2/vn2/vt2 ... - coords + normals + tex coords
4: f v1//vt1 v2//vt2 ... - coords + tex coords

You can see how the omit the normals if you don't need them.

I didn't read much about the materials, but a texture map is optional, so you don't necessarily have to specify the stuff for the other properties.

[porimac]

Thank you for your complement to my bad explanation, finale00.
Your post are informative for me, too.

[Riigel]

I have another question about texture mapping.

I have extracted a game Model (soccer ball). It's using 2 textures, one normal and one alpha texture. The problem is, that both use different
texture coordinates(vt). Is it possible to use both textures with the obj fileformat?

@finale00
thx for your hints, they helped me alot.
There is a little mistake in your post.

There are 4 different face definitions.

1: f v1 v2 v3 - just coords
2: f v1/vn1 v2/vn2 v3/vn3 - coords + normals
3: f v1/vn1/vt1 v2/vn2/vt2 ... - coords + normals + tex coords
4: f v1//vt1 v2//vt2 ... - coords + tex coords

2: f v1/vn1 -> coords + tex coords.
4: f v1//vt1 -> coords + normals.

[finale00]

Ya, I probably should've checked the order before I wrote it
I don't know anything about texturing so I can't help there.