AP_Scripting: applet for Plane follow on a switch

[timtuxworth]

DRAFT for comment.
This builds on the existing plane_guided_follow.lua example. It adds speedup/slowdown so the following vehicle can "catch up" with the target and prevents guided mode from attempting to loiter around the target vehicle when it gets close. Also adds FOLL_ACT_FN so that an RC switch can be used to trigger/exit the follow.

Note the change to GCS_Mavlink.cpp, without this one line in handle_command_int_do_reposition to set plane.guided_state.target_heading_type = GUIDED_HEADING_NONE, nothing works. With this line, like magic - follow!

Updated, but still draft. Re-written to use the new MAVLink/Lua interface in #27365

Includes a Lua module for a "PI" controller. This is basically just extracted as is from the plane_aerobatics.lua and generalized so it can be used without copying. Ideally "D" would be added.

[IamPete1]

The scripting checks are also reporting:

    libraries/AP_Scripting/applets/plane_follow.lua:20:7: unused variable ALT_FRAME_ABSOLUTE
    libraries/AP_Scripting/applets/plane_follow.lua:75:7: unused variable have_target
    libraries/AP_Scripting/applets/plane_follow.lua:118:7: empty if branch
    libraries/AP_Scripting/applets/plane_follow.lua:132:10: unused variable target_sysid
    libraries/AP_Scripting/applets/plane_follow.lua:145:10: unused variable vehicle_location
    libraries/AP_Scripting/applets/plane_follow.lua:152:21: value assigned to variable target_offsets is overwritten on line 153 before use

[Hwurzburg]

this needs a GCS text announcing that its been loaded, like we do in other applets

[timtuxworth]

This is a draft for comm

this needs a GCS text announcing that its been loaded, like we do in other applets

Done

[timtuxworth]

libraries/AP_Scripting/applets/plane_follow.lua:152:21: value assigned to variable target_offsets is overwritten on line 153 before use

I have to call two methods on AP_Follow to get all the values I need and both of them return target_offsets. Do you think I should refactor the code in AP_Follow so I can call a single method?

[timtuxworth]

The scripting checks are also reporting:

How can I run these checks myself?

[IamPete1]

How can I run these checks myself?

This should work:

apt install lua-check
./Tools/scripts/run_luacheck.sh 

You can also run the new checks with:

python ./Tools/scripts/run_lua_language_check.py