Make fragment fusion script compliant with multiple Open3D versions.

[SergioRAgostinho]

The current PR addresses API changes that occurred in Open3D. Three important points to mention here:

• exposed the reduced name o3d to the entire because it's being used in more than one function scope.
• Open3D's version is checked only once and a proxy function object is assigned the correct function signature.
• I've checked the documentation on the website and write_point_cloud is always under o3d.io from 0.6.0 onward. There's no docs on the project's website for any version prior to it.

[XuyangBai]

Hi, thank you for your feedback. I didn't test the open3d with version later than 0.7 but line 22 should be

if LooseVersion(o3d.__version__) > LooseVersion("0.7.0.0"):

or the version 0.7.0.0 will be in the wrong branch

[SergioRAgostinho]

I am not witnessing that behaviour.

>>> import open3d as o3d
>>> from distutils.version import LooseVersion
>>> o3d.__version__
'0.9.0.0'
>>> LooseVersion(o3d.__version__) >= LooseVersion("0.9")
True
>>> LooseVersion(o3d.__version__) >= LooseVersion("0.9.0.1")
False
>>> LooseVersion(o3d.__version__) >= LooseVersion("0.10")
False
>>> LooseVersion(o3d.__version__) >= LooseVersion("0.9.1.0")
False
>>> LooseVersion(o3d.__version__) >= LooseVersion("0.9.0.0")
True
>>> LooseVersion(o3d.__version__) >= LooseVersion("0.7.0.0")
True
>>> LooseVersion(o3d.__version__) >= LooseVersion("0.7")
True

What's your distutils version? Mine is 3.6.10.

Interesting. The inequality sign is key to the problem, you can see below.

>>> LooseVersion(o3d.__version__) > LooseVersion("0.9")
True    # It should be false, but subject to interpretation.
>>> LooseVersion(o3d.__version__) > LooseVersion("0.9.0.1")
False
>>> LooseVersion(o3d.__version__) > LooseVersion("0.10")
False
>>> LooseVersion(o3d.__version__) > LooseVersion("0.9.1.0")
False
>>> LooseVersion(o3d.__version__) > LooseVersion("0.9.0.0")
False 
>>> LooseVersion(o3d.__version__) > LooseVersion("0.7.0.0")
True
>>> LooseVersion(o3d.__version__) > LooseVersion("0.7")
True

However in the patch I submitted I'm using >= and not >. Thus things are falling under the right branch. Do you still want me to modify the version to the complete semver string?

[XuyangBai]

@SergioRAgostinho There might be something wrong with distutil. In my environment, things go wrong if using 0.7.0.0 version. My >= and > return different values.

Maybe just leave it as so, I use open3d 0.7.0.0 for my whole project and it takes time to make it all compliant with other versions. Anyway, thank you so much !

[SergioRAgostinho]

Maybe just leave it as so, I use open3d 0.7.0.0 for my whole project and it takes time to make it all compliant with other versions. Anyway, thank you so much !

No problem.