Support straight line mission landings #23576

RomanBapst · 2024-08-20T07:41:48Z

Solved Problem

When flying Fixed Wings in a space constrained area, it can be difficult to plan the usual orbit type mission landings.
There might simply not be enough space for the vehicle to orbit while it's descending in altitude.

Of course, one can just plan a mission with simple waypoints and add a VTOL LAND waypoint at the end. However, there is always the risk that the altitude difference between the waypoints is too big and the vehicle cannot follow the glide-slope, causing it to loiter at the next waypoint in order to reduce altitude further. This behavior is highly undesirable as part of a mission landing, as already explained above.

Fixes #{Github issue ID}

Solution

I propose a solution where all simple waypoints AFTER a land stark marker have their altitude acceptance radius set to INFINITY, which will cause the guidance logic to track altitude for these waypoints based on best effort.

Changelog Entry

For release notes:

Feature
Documentation: Add documentation for QGC explaining the difference between the two types of landings.

Test coverage

Tested regularly in production but on a much older branch. Only SITL tested on main.

Context

Altitude profile for staright line landing. Notice, that for the first waypoints the altitude needs to reached, however, for the last waypoints (landing pattern), the altitude is not reached anymore, but the waypoint is still accepted.

src/modules/navigator/mission_block.cpp

wing guidance - allows navigator to explicitly set the altitude acceptance radius - needed for staright line landing support * added ignore_alt_acceptance to position setpoint message to allow guidance logic to ignore altitude error on waypoint - can be useful to prevent loitering at a waypoint within a mission landing sequence Signed-off-by: RomanBapst <bapstroman@gmail.com> * Update src/modules/fw_pos_control/FixedwingPositionControl.cpp Co-authored-by: Alvaro Fernandez <alvaro@auterion.com> * fixed typo Signed-off-by: RomanBapst <bapstroman@gmail.com> --------- Signed-off-by: RomanBapst <bapstroman@gmail.com> Co-authored-by: Alvaro Fernandez <alvaro@auterion.com>

KonradRudin · 2024-08-20T09:08:01Z

I guess the small bump in altitude after accepting the last waypoint is due to the transition?

src/modules/navigator/mission_block.cpp

src/modules/fw_pos_control/FixedwingPositionControl.cpp

src/modules/navigator/mission_block.cpp

ryanjAA · 2024-08-25T12:37:11Z

~~I'm trying to wrap my head around this.~~

I do recall (and use to use) straight line landings way back on <1.8? (when you put it back in in 1.04-ish) but that aside, you come in for landing and just plan a path basically and the idea here is that it just follows the path and max descent until we hit the ground but aren't constrained to hitting the WP alts on the path? Is that correct?

~~Is this somewhat similar to how Land mode works (in FW) but just with the benefit of being able to plan a path rather than say land now?~~

Edit: ya makes sense...

sfuhrer

I would look into passing an "disregard altitude acceptance" flag from the groundstation to PX4 in cases where it should be ignored (e.g. during VTOL_LAND items). I don't think it should apply to every landing sequence.

src/modules/navigator/mission_block.cpp

src/modules/navigator/mission.cpp

src/modules/navigator/rtl_direct_mission_land.cpp