Snapshot fields

A snapshot is one look at a session, built from the latest MAVLink message of each type the pump thread has received. snapshot returns one on demand. wait_until, arm, set_mode, disarm, set_speedup, set_wind and every step result carry one too.

The session asks SITL for these streams on top of the defaults: HEARTBEAT at 4 Hz, ATTITUDE, VFR_HUD and SERVO_OUTPUT_RAW at 10 Hz, SYS_STATUS, BATTERY_STATUS, MISSION_CURRENT and EXTENDED_SYS_STATE at 2 Hz, and SITL’s own truth (SIMSTATE, SIM_STATE) with SYSTEM_TIME at 20 Hz. A field whose message has not arrived yet is null.

Snapshot

Field	Type	Meaning
`session_id`	`str`
`state`	`str`	starting, open, died or closed
`seq`	`int`	messages received so far; pass as since_seq to `wait_until`
`t_sim_s`	`float`	autopilot time since boot, s
`speedup`	`float`	the speed SITL is running at now
`viewers`	`int`	people watching the live video feed; while any do, the session runs no faster than real time (idle pacing still applies)
`instance`	`int \| None`
`armed`	`bool`
`mode`	`str \| None`
`mode_since_s`	`float \| None`	sim time the autopilot's reported mode last changed to this one
`height_m`	`float`	above the pad since arm, else above home
`lat`	`float \| None`
`lon`	`float \| None`
`roll_deg`	`float \| None`
`pitch_deg`	`float \| None`
`yaw_deg`	`float \| None`
`airspeed_mps`	`float \| None`
`groundspeed_mps`	`float \| None`
`climb_mps`	`float \| None`
`throttle_pct`	`float \| None`
`volts`	`float \| None`
`amps`	`float \| None`
`mah`	`float \| None`	consumed charge since the last battery reset
`landed`	`bool \| None`	from EXTENDED_SYS_STATE; None until it arrives
`mission_seq`	`int \| None`	current mission item (MISSION_CURRENT)
`rc`	`list[int]`	RC override this server sends, channels 1 to 8
`servo`	`list[int] \| None`	SERVO_OUTPUT_RAW channels 1 to 8
`texts`	`list[Text]`	latest STATUSTEXTs, oldest first
`wind`	`dict \| None`	the session's wind: mean, gusts, the gust now and what SITL got
`error`	`str \| None`	why the session died, if it did

seq counts every message the session has received. It only grows, which is what makes it useful as since_seq.

height_m comes from SITL’s true position (SIM_STATE), measured from the pad, once the session has armed; before the first arm it is the autopilot’s own height above home. rc is what this server sends as RC override, not what the autopilot’s mixer chose; servo is the autopilot’s output.

wind, when the session has one, holds the mean wind, the gust settings, gust_mps (the gust now, along, across and up) and sitl (the SIM_WIND_SPD, SIM_WIND_DIR and SIM_WIND_DIR_Z SITL was last given).

A snapshot from a hover on the stock quadplane, with texts=1. volts reads 0 because the stock parameters configure no battery monitor.

{
  "session_id": "d79353", "state": "open", "seq": 8767, "t_sim_s": 67.961, "speedup": 0.05,
  "instance": 40, "armed": true, "mode": "QLOITER", "mode_since_s": 10.264,
  "height_m": 7.37, "lat": -35.3632629, "lon": 149.1652371,
  "roll_deg": 0.11, "pitch_deg": -0.19, "yaw_deg": 355.45,
  "airspeed_mps": 0.92, "groundspeed_mps": 0.022, "climb_mps": -0.008, "throttle_pct": 59.0,
  "volts": 0.0, "amps": null, "mah": null, "landed": false, "mission_seq": 0,
  "rc": [1500, 1500, 1500, 1500, 1800, 1500, 1500, 1500],
  "servo": [1500, 1500, 1000, 1500, 1750, 1750, 1750, 1750],
  "texts": [ { "seq": 6329, "t_sim_s": 49.563, "text": "Throttle armed" } ],
  "wind": null, "error": null
}

Text

One autopilot STATUSTEXT, with the seq it arrived at. The session keeps the latest 200.

Field	Type	Meaning
`seq`	`int`
`t_sim_s`	`float`
`text`	`str`