Subsystem/ins

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INS subsystem

The INS (Inertial Navigation System) subsystem specifies which position and velocity estimation algorithm you are using.

Most of the INS filters are only providing position and speed, and they need to be used together with an AHRS (Attitude and Heading Reference System) filter for attitude. Currently, only the experimental invariant filter is a full INS.

Currently possible INS subsystem types are:

Type Point Type Firmwares Notes
alt_float floating fixedwing
gps_passthrough all
xsens all external
xsens700 all external
no_type all
Horizontal Filter Float (hff) floating
extended floating? all
vectornav all external
float_invariant floating all


e.g. for the extended filter:

File: conf/airframes/myplane.xml
  <firmware name="fixedwing or rotorcraft">
     ...
    <subsystem name="ins" type="extended"/>
  </firmware>

Implementations

alt_float

Filters altitude and climb rate for fixedwings.

A 2-state Kalman filter that estimates vertical position and vertical velocity from GPS and barometric data.

When USE_BAROMETER is defined to TRUE:

  • GPS horizontal position and horizontal velocity is directly passed through
  • GPS vertical position sets the altitude for the barometric reference pressure (QFE)
  • Vertical position and velocity is a filtered based on barometric pressure with respect to the reference pressure and GPS vertical velocity readings.

When USE_BAROMETER is not defined, FALSE or 0:

  • GPS velocity is directly passed through to the vehicle's state.
  • GPS horizontal position is directly passed through.
  • Altitude is filtered based on GPS height and vertical velocity data.

Parameters

USE_BAROMETER - Enables the use of barometric data

DEBUG_ALT_KALMAN - Enables debug messages from the subsystem (Default: not defined)

e.g. to use with barometer:

File: conf/airframes/myplane.xml
  <firmware name="fixedwing">
     ...
    <subsystem name="ins" type="alt_float">
      <define name="USE_BAROMETER" value="TRUE"/>
    <subsystem>
  </firmware>


GPS passthrough (gps_passthrough)

"dummy" INS that does no filtering whatsoever. It directly passes GPS position and velocity through.

File: conf/airframes/myplane.xml
  <firmware name="fixedwing or rotorcraft">
     ...
    <subsystem name="ins" type="gps_passthrough"/>
  </firmware>

xsens

XSens Mti-G

File: conf/airframes/myplane.xml
    <subsystem name="ins" type="xsens">
      <configure name="XSENS_UART_NR" value="0"/>
      <configure name="XSENS_UART_BAUD" value="B115200"/>
    </subsystem>

xsens700

XSens Mti-G

File: conf/airframes/myplane.xml
    <load name="ins_xsens_MTiG_fixedwing.xml">
      <configure name="XSENS_UART_NR" value="0"/>
    </load>

no_type

Vertical filter (in float) estimating altitude, vertical velocity and accelerometer bias.

If USE_GPS, horizontal position and velocity is set directly by GPS.

File: conf/airframes/myplane.xml
  <subsystem name="ins"/>

Horizontal Filter Float (hff)

simple with float vertical and horizontal filters for INS

File: conf/airframes/myplane.xml
  <firmware name="fixedwing or rotorcraft">
     ...
    <subsystem name="ins" type="hff"/>
  </firmware>

extended

Extended vertical filter (in float).

A 4-state Kalman filter that estimates:

  • vertical position
  • vertical speed
  • accelerometer bias
  • barometric offset
File: conf/airframes/myplane.xml
  <firmware name="fixedwing or rotorcraft">
     ...
    <subsystem name="ins" type="extended"/>
  </firmware>

Parameters

INS_PROPAGATE_FREQUENCY - Defines the frequency (Hz) of the propagation model (Default: PERIODIC_FREQUENCY)

vectornav

Driver for the Vectornav VN-200 INS, see also Sensors/imu#Vectornav_VN-200.

float_invariant

A full INS estimating attitude, velocity, position and biases via invariant filter