Plane: add radius for GUIDED mode

[magicrub]

Allow setting a radius specifically for mode GUIDED via mavlink. A radius of Zero indicates to use WP_LOITER_RAD which is the existing behavior

[IamPete1]

How about a negative radius for a CCW loiter?

[magicrub]

How about a negative radius for a CCW loiter?

Still works. I don't know what the usual guided command mode is, but I/we use a loiter command (loiter_unlim in our case) which handles that by setting the loiter_CCW bit on the location

[pompecukor]

Allow setting a radius specifically for mode GUIDED via mavlink. A radius of Zero indicates to use WP_LOITER_RAD which is the existing behavior

Can you maybe also add a separate parameter for this? GUIDED_LOITER_RAD.
This would be really useful. We know from experience that SAR and Security users mostly need large radius on guided mode as the "observe/search". And for this reason we kept having the put unnecessarily large WP_LOITER_RAD. Another adverse effect is if the change the radius during the mission (like 500m) then forget about it and do a loiter to alt, which again would use such a big radius. The Loiter Rad in Mission planner would be controlling this instead of the WP loiter rad, which typically one would not be wanting to change on the fly.

[peterbarker]

I really don't like the use of sending through these mission_item messages when we have so many other more appropriate messages we can use. AFAICS we're completely ignoring what sort of command is being passed in here....

I can think of two other approaches we can take off the top of my head. The first is to flesh out support for MAV_CMD_NAV_LOITER_UNLIM. Currently on Plane this just changes mode to loiter, ignoring all other fields in the message, like where-to-loiter-at and the loiter radius - the following PR changes that to honour these fields:
https://github.com/peterbarker/ardupilot/pull/new/wip/loiter-unlim-location-radius . Here is a branch for MAVProxy which adds support for the concept: https://github.com/peterbarker/MAVProxy/pull/new/wip/loiter-unlim-location-radius Note that neither of these branches are in good working order, particularly when it comes to altitude, but you can right-click on the map in MAVProxy and have it fly to somewhere and loiter at a user-supplied radius. The instantly-change-to-guided-mode-when-command-received is perhaps not in good taste but is much less likely to break people currently sending the command to ArduPlane.

The second approach - and the one I think I prefer - is to add support for MAV_CMD_DO_CHANGE_RADIUS. A GCS wishing to have the vehicle fly to a location and loiter at 400m would first send a MAV_CMD_DO_REPOSITION and if that is accepted follow it up with a MAV_CMD_DO_CHANGE_RADIUS to set the loiter radius at the other end.

[magicrub]

After a rethink, this PR is definitely not the correct way forward. MAV_CMD_DO_REPOSITION is the proper way to use guided and adding radius should be done in one, or all, of the below methods in a new PR:

1. add CMD_DO_REPOSITION.param3 = radius
2. add MAV_CMD_DO_CHANGE_RADIUS, maybe with a enum param to specify which radius: WP loiter, loiter mode, guided, RTL
3. add a new Guided WP Radius param