Add support for MAV_CMD_DO_ORBIT

[peterbarker]

Companion to ArduPilot/ardupilot#33525

[tridge]

Automated review note — AI-generated (Claude), validated against the live diff. Please sanity-check before acting.
Full report: https://uav.tridgell.net/DevCallReviews/2026_09_01_AIReview/devcall_pr_reviews.html#prMAVProxy-1702

Reviewed at head 145e62aa3e. COMMENT — no blockers.

The parameter mapping is correct, which is the thing most worth getting right here and the easiest to get wrong. Checked field by field against the fetched common.xml: p1 radius in metres with "Positive: orbit clockwise. Negative: orbit counter-clockwise." passed through signed and documented that way in your help text; p2 velocity m/s with NaN meaning vehicle default; p3 mapped to the ORBIT_YAW_BEHAVIOUR enum values; p4 declared units="rad" and correctly converted from circuits as orbits * 2 * pi (verified: 3 circuits → 18.8495559 = 6π); p5/p6 scaled to degE7 in a COMMAND_INT. COMMAND_INT is right given the lat/lon, and the non-_INT frame constants are correct — the spec marks the _INT variants superseded since 2024-03.

Two things worth fixing:

1. velocity= and yaw= raise an uncaught ValueError from a GUI-reachable path. Both are declared type=str in orbit_arg_spec, so the arg parser's try/except ValueError never sees them and the later float(...) raises. Reachable by simply clearing the free-text "Velocity (m/s)" box in the Orbit Here dialog; the user gets ERROR in command [...] : could not convert string to float: '' with no usage. (mavproxy_mode.py:248, :258)
2. No mode change is requested and the NACK isn't surfaced. cmd_guided sends DO_REPOSITION with MAV_DO_REPOSITION_FLAGS_CHANGE_MODE; cmd_orbit has no equivalent and nothing reads COMMAND_ACK, so from Loiter it just fails with a generic console line a map-menu user is unlikely to be watching.

That second point matters more than usual because no released ArduPilot firmware implements this command yet — a search of a full checkout finds DO_ORBIT only in the bundled mavlink XML, zero source files. The only implementation is the still-open ArduPilot/ardupilot#32434 (Copter-only, Guided-only, size-gated), so today every vehicle NACKs this. Worth cross-linking the two PRs in the description.

Smaller: negative orbits emits a negative p4, below the spec's minValue="0" (ArduPilot's handler fabsf()s it, but another stack may not); yaw=Default sends NaN for p3, which the spec doesn't annotate as NaN-capable — ORBIT_YAW_BEHAVIOUR_UNCHANGED is its actual "leave it alone" value; and frame= permanently rewrites the shared flytoframe setting, which the Orbit Here popup always emits, so every map orbit silently reassigns the frame Fly To will use next.