collision warning algorithms

moshe-braner / SoftRF

:airplane: Multifunctional, compatible DIY general aviation proximity awareness system

GNU General Public License v3.0

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collision warning algorithms #3

Closed moshe-braner closed 5 months ago

moshe-braner commented 2 years ago

Try and improve the algorithms:

review current code for when same traffic is warned about again.
proximity method should have hysteresis: after a warning, require same target to be at a larger distance for a while before issuing a new warning.
vector method may not be working: stationary targets trigger alarms as soon as visible. Experiment with moving targets. If still a problem, then need to revise vector algorithm itself.

moshe-braner commented 2 years ago

Added code (mostly in TrafficHelper.cpp but also tweaked TrafficHelper.h, Legacy.h, NMEA.cpp, SoftRF.h) to give a new audio alert if a target got two levels closer than previous alert, or got two levels farther and then back to same level again. This required adding a "CLOSE" level between NONE and LOW. Tweaked NMEA.cpp to restore level codes sent out as data to other devices to the previous codes, since apparently the alarm level codes are an external standard.

moshe-braner commented 2 years ago

Additional modifications made to traffic alarms:

adjust the distance between aircraft by some multiple of altitude difference for the purpose of deciding what is close enough to trigger an alarm.
same for the "vector" alarm method, this results in a modified "time until collision".
also use that modification for the purpose of deciding which traffic is "closer" when overwriting old traffic with new.
Modified vector method to use two relative-bearing angle thresholds, with different alarm levels (for same time-to-collision). The threshold angle (now) defined in TrafficHelper.h, and double that.
Moved the vector method constants to TrafficHelper.h

moshe-braner commented 2 years ago

Because there is some error in the GPS altitude, and also some devices will use GPS altitude while others use barometric altitude, I have adjusted the code to subtract 60 meters from the absolute altitude difference (if it's more than 60). That is so that a possible real collision danger will not get ignored. The remainder is multiplied by "SLOPE" (5) and added to the distance to determine alarm level and target priority.

moshe-braner commented 2 years ago

Added code in NMEA.cpp to take altitude differences into account also in the choosing of the "high priority" target for NMEA export.

moshe-braner commented 2 years ago

Version 04: in TrafficHelper.cpp added adjustment to altitude difference based on relative vertical speed. For example, if one glider is climbing in a thermal, and another is flying towards the thermal in sink, and is higher - by the time they may collide the altitude difference between the gliders will get smaller, so be more inclined to sound an alarm.

Also re-organized ParseData() to clarify what it is doing and also make it a bit more efficient.

moshe-braner commented 2 years ago

Version 07: finally implemented collision prediction based on extrapolating circular paths. This uses the data sent by FLARMs, or converts the data sent by other protocols. Choose "Legacy" alarm method. Also transmits data compatible with FLARMs if "Legacy" protocol chosen. This is new draft code and needs flight testing.