[PPRZ Center] Add @AIRCRAFT placeholder constant.

[esden]

When you use @aircraft as a constant parameter to a program in your
session, it will be automatically replaced by the name selected in the
A/C dropdown combo box of the Paparazzi Center. This makes it possible
to create generic sessions that start programs which need to know which
aircraft is of interest. For example settings.

This is a possible solution to the #1215 issue.

[edit] Changed the comment here to reflect the final patch, decrease confusion.

[gautierhattenberger]

I would prefer @AIRCRAFT as keyword to be consistent with other variable parameters in airframe file.

[esden]

I agree, I have amended the patch to reflect that. :)

[fvantienen]

Coul we maybe also add an aircraft id? Since some programs use that (like natnet2ivy).

[esden]

Can you point me to an example session that uses natnet2ivy, so I can add it too?

Why is natnet2ivy using the ID, most tools are using the aircraft name instead. Should it not be consistent with the rest of tools and use the name?

[gautierhattenberger]

I know I'm being annoying :), but we usually use AC_ID to point to the aircraft ID

[fvantienen]

Because natnet2ivy is written in c and doesnt parse the xml files.
I wanted to be consistent at the start but didn't want to put time in a xml parser in c.

Example session:
natnet2ivy -ac @AC_ID 1

[esden]

@gautierhattenberger So we use @aircraft and @AC_ID? That is not very consistent euther... Unless we use @ac and @AC_ID.

@fvantienen This is off topic of this pull request, but I think you should use a small xml parser still, and maybe create a library that implements getters for simple items. I am sure there will be more C programs in the future, so creating facilities for those is a very good idea. (libpprz.so) We use the name of the aircraft throughout the ground system to stay consistent, so we should stay in that habit I think.

[gautierhattenberger]

It is consistent in the way that we use AIRCRAFT to give the name of plane to the makefile rule in order to compile the airborne code and we use AC_ID to get the numerical id in the airborne code itself.
It is not like this choice is the best, but I don't think changing it is a good idea now.

[flixr]

I agree with @gautierhattenberger here...
Also wondering how the added session should be named, it is called "setup actuators" now, but it not in the least specific to that. It's just messages and settings...

[esden]

Raw Settings?
No GCS Settings?
Raw Messages and Settings?
...

the setup actuators is descriptive in the sense that this is the intended purpose at the moment. It should be superseded by a dedicated script that does not use settings for this but has an easier to use interface for that particular purpose.

[flixr]

@esden could you plz change AIRCRAFT_ID to AC_ID as @gautierhattenberger suggested?
Also maybe disable the logging in server for the "setup actuators" session?
I would vote to name the session "Messages and Settings" or something like that...

[esden]

@flixr sorry, I was convinced that I already did fix the AC_ID part. None the less I have made all the suggested changes and pushed an updated patch set.