Conversion to OBJ File

This section will show you how you can convert IndexedFaceSet and Surface datastructures into OBJ files.

Indexed Face Set to OBJ file

In order to store an indexed face set in an OBJ file it is mandatory to have a coordinate attribute representing the 3D coordinates of the vertices.

>>> import ddg
>>> from ddg.indexedfaceset import IndexedFaceSet as IFS
>>> import numpy as np
>>> surf = IFS([[0, 1, 2], [3, 4, 5], [6, 7, 8]])
>>> co = np.arange(27).reshape((9, 3))
>>> surf.set_attribute("co", "verts", co)

To convert an indexed face set to an OBJ file use the function ifs_to_obj():

ddg.conversion.obj.ifs.ifs_to_obj(ifs, obj_name, file_location, attribute_name='co')

Convert an IndexedFaceSet to an obj wavefront format.

Parameters:

ifsddg.indexedfaceset.IndexedFaceSet

obj_namestring

Name of the surface in the obj file

file_locationstring

Path to where the obj file should be saved

attribute_namestring (default=”co”)

Name of the IndexedFaceSet vertex attribute storing the coordinates

Returns:

None

It can be used as easy as

>>> from ddg.conversion.obj.ifs import ifs_to_obj
>>> example_ifs = ddg.indexedfaceset.cube()
>>> object_name = "sample_obj"
>>> file_location = "path-to-file/sample_obj_file.obj"
>>> ifs_to_obj(example_ifs, object_name, file_location, "co")  

This will generate a file with the following content.

# generated with pyddg library.
o sample_obj
v 1.0000 1.0000 1.0000
v 1.0000 -1.0000 -1.0000
v -1.0000 1.0000 -1.0000
v -1.0000 -1.0000 1.0000
f 1 2 3
f 3 4 1
f 2 4 3
f 1 4 2

Note

In an OBJ file vertex indices start at 1. In the IFS datastructure vertex indices start at 0. Thus, the vertex indices of the resulting OBJ file will contain an offset of 1.

With o the object name, v representing the vertices and f representing the faces with vertex indices.

Note

OBJ files can also contain texture and normal coordinates, vt and vn, for vertices. These belong to pairs of the form (vertex, face). Such pairs can’t be handled by IndexedFaceSet. Thus, a resulting OBJ file will only contain vertex coordinates and therefore only faces of the form f 1 2 3.

Halfedge to OBJ File

Similarly, to convert a Surface to an OBJ file use hds_to_obj():

ddg.conversion.obj.halfedge.hds_to_obj(surface, filename='obj_file.obj', co_attr='co')

Converts a ddg.halfedge.Surface to an obj file.

If ‘vn’ and/or ‘vt’ are given as halfedge attributes, they will be

written in the obj file format.

The vertices need to have an attribute storing the coordinates.

Results in obj file with given v and faces of the form f 1 2 3

or given v,vt and faces of the form f 1/1 2/1 3/1

or given v,vn and faces of the form f 1//1 2//1 3//1

or given v,vt,vn and faces of the form f 1/1/2 2/1/2 3/1/2.

Vertices will be ordered by indices and vt and vn coordinates in increasing order.

Parameters:

surface: ddg.halfedge.Surface

halfedge data structure to be converted

filenamestr (default=’obj_file.obj’)

Name for the resulting obj file a file path can be specified here default is ‘obj_file’ which will be saved in the cwd

co_attrstr (default=’co’)

string of the vertx attribute that stores the coordinates

Notes

• Indexing in obj files starts at 1.

>>> import ddg
>>> from ddg.conversion.obj.halfedge import hds_to_obj
>>> example_surface = ddg.halfedge.tetrahedron()
>>> file_location = "path-to-file/sample_obj_file.obj"
>>> hds_to_obj(example_surface, file_location, "co")  

Which will generate a file with the following content.

Obj file created by halfedge data structure

v 1 1 1
v 1 -1 -1
v -1 1 -1
v -1 -1 1

f 1 2 3
f 1 4 2
f 2 4 3
f 3 4 1

Warning

This conversion does not support an object_name.

If vt and/or vn were given as (half)edge attributes, the corresponding values are written to the OBJ file and the face values are changed accordingly.