Read multiple objects from an obj file

[Salingo]

I have a question about reading multiple objects in Wavefront .obj files, the obj files may contain many object groups such as:

#
# object example_1
#
v 0.0 0.0 0.0
v 1.0 0.0 0.0
v 1.0 0.0 1.0
v 0.0 0.0 1.0
# 4 vertices

g example_1
f 1 4 3 
f 3 2 1 
# 2 faces

#
# object example_2
#
v 2.0 2.0 2.0
v 3.0 2.0 2.0
v 1.0 1.0 3.0
v 2.0 2.0 2.0
# 4 vertices

g example_2
f 1 4 3 
f 3 2 1 
# 2 faces

The igl::readOBJ function only returns one single object, so the group information is lost. Is there an easy way to read this kind of obj file as grouped objects?

[jdumas]

Well I suppose you can use igl::facet_components() and igl::remove_unreferenced() to extract each connected component (supposing you have one per object), and then remove vertices that do not belong to each object.

[alecjacobson]

(@jdumas, groups are different from connected components)

@Salingo , no. libigl .obj io does not support groups.

[jdumas]

Oh ok. I didn't know you could store a scene in a single .obj file.

[alecjacobson]

there's a lot of crazy stuff you can do in a .obj ... For example, we also don't support negative indices.

[Salingo]

@alecjacobson @jdumas Many thanks! I modified the readOBJ file and now group objects can be loaded.

[QhelDIV]

@alecjacobson @jdumas Many thanks! I modified the readOBJ file and now group objects can be loaded.

I wonder how to edit it. Could you please share your code?

[Salingo]

@alecjacobson @jdumas Many thanks! I modified the readOBJ file and now group objects can be loaded.

I wonder how to edit it. Could you please share your code?

Sure, just change '.txt' to '.h'.
:D
read_groupOBJ.txt

[QhelDIV]

@alecjacobson @jdumas Many thanks! I modified the readOBJ file and now group objects can be loaded.

I wonder how to edit it. Could you please share your code?

Sure, just change '.txt' to '.h'.
:D
read_groupOBJ.txt

Great! Thanks a lot.