Parse file:// mesh prefix from mesh filepath

[IDavGal]

Address changes mentioned in this issue.

• Add support for parsing out the file:// required by rViz from mesh filepaths
• Normalizes absolute paths after parsing out the prefixes, since when present, the filepath would be considered as relative (filepath starts without /)

[omichel]

The file URI scheme doesn't allow for relative paths. See explanations here. Relative paths should be expressed without the file:// prefix. Also, absolute paths without a host name should be expressed with three /, e.g. file:///path/to/my_file.txt. Do you have any example of URDF file that features some file:// URI references?

[IDavGal]

I've encountered this issue when working with an URDF with a workaround for gazebo in ROS 2.

Unrelated, but apparently there is an issue when spawning a robot using gazebo_ros in ROS 2, specifically with mesh filenames using the package:// prefix.
There is a discussion regarding this issue here.
Using file://$(find ) extends to an expression similar to file:///path/to/my/file as you mention.

The URDF I mention can be found here

[omichel]

I see, therefore, I believe we should support the file:/// protocol which is generated by xacro from the file://$(find syntax.

[omichel]

That would seem clearer and cleaner to me:

Suggested change

	if meshfile.count('package'):
	idx0 = meshfile.find('package://')
	meshfile = meshfile[idx0 + len('package://'):]
	elif meshfile.count('file'):
	idx0 = meshfile.find('file://')
	meshfile = meshfile[idx0 + len('file://'):]
	if not os.path.isabs(meshfile):
	# Use the path relative to the output file
	meshfile = os.path.normpath(os.path.relpath(os.path.join(path, meshfile), outputDirectory))
	if meshfile.startswith('package://'):
	idx0 = meshfile.find('package://')
	meshfile = meshfile[idx0 + len('package://'):] # package relative path
	elif meshfile.startswith('file:///'):
	idx0 = meshfile.find('file:///')
	meshfile = meshfile[idx0 + len('file://'):] # we keep the last slash for absolute path
	elif not os.path.isabs(meshfile):
	# Use the path relative to the output file
	meshfile = os.path.normpath(os.path.relpath(os.path.join(path, meshfile), outputDirectory))