OpenNI apps: Improve handling of command line arguments

[filbert14]

Edit: Done! Sorry, I didn't know drafts were a thing. .

Side notes:

• I modified usage() in openni_color_filter.cpp as well as openni_tracking.cpp to fit the rest of the files (default values as well as structure)
• I think there is a typo in parse.h at line 212
• Now that device id is optional (or as it turns out, a lot of cmd line args seem to be optional), do you think it would be a good idea to update the syntax for usage()? (Like in the previous version of openni_color_filter.cpp - [] for optional params, < and > for required params, etc.)

General changes are (just a checklist to ease the review):

• being more flexible with argument count (tolerance when nothing is being passed since everything would default anyway, so no more if (argc < 2)
• let device_id be an optional parameter initialized with an empty string, and update args to device_ids
• and update usage() to fit the actual usage

[larshg]

klt and grab_images feel like they would be a bit challenging to refactor, please inform me if that's on the table ;)

Then perhaps we should do that in a new PR 👍

[filbert14]

You are right - sorry, I must have been extremely sleepy

in any case, deal! I will work on it after this is merged, thanks for the review :)

[larshg]

@sfilbertf could you please rebase and then I think its 🚀

[filbert14]

Hey, I think it should be done :)

[mvieth]

I think it's a bit problematic that, if users update PCL but try to use the old syntax app_name <device_id> instead of the new app_name -device_id <device_id>, the device id given as the first command line argument will not be used and the user will not even know about it. How about the following: call parse_argument for -device_id, if the argument is not found and argc > 1 and argv[1] does not start with a -, then use argv[1] as the device id. So perhaps like this:
if(pcl::console::parse_argument(argc, argv, "-device_id", device_id) == -1 && argc > 1 && argv[1][0] != '-') device_id = argv[1];

[mvieth]

Thank you!