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Safehome and Auto-land#

One of the great features of INAV 2.6 was the safehome capability. The user can define of set of up to eight locations, and if any of these is within 200m (configurable up to 650m in INAV 2.7), then that is used as the home location for RTH (and RTH failsafe).

INAV setting#

safehome is set in INAV using the CLI, (note more recent Configurators also have a UI); here's an example:

# safehome
safehome 0 1 508047750 -14948970
safehome 1 1 509102384 -15344850
safehome 2 1 509390336 -14613540
safehome 3 1 509149619 -15337365
safehome 4 0 508054891 -14961431
safehome 5 0 543545392 -45219430
safehome 6 0 540954148 -47328458
safehome 7 0 0 0

As you see, it's not too user friendly; the parameters are

  • Index (0 - 7)
  • Status (0 = don't use, 1 = can use)
  • Latitude as degrees * 10,000,000 (i.e. 7 decimal places)
  • Longitude as degrees * 10,000,000 (i.e. 7 decimal places)

It can be error prone to get locations into the correct format, particularly when a common source (Google Maps) only provides 6 decimal places of precision.

mwp solution#

Graphical User Interface#

Legacy Images

The images this section are from legacy mwp, however the capability is the same.

Note: Since mwp 7.32.?, mwp provides additional fields for the Autoland function that first appeared in INAV 7.1.0.

mwp now offers a Safe Homes menu option:

mwp safehome

This will launch the Safe Home window:

mwp safehome

From here it is possible to:

  • Load safehomes from a file in CLI format. A CLI diff or dump can be used.
  • Save safehomes to a file in CLI format. If a CLI diff or dump is selected, then only the safehome and fwapproach stanzas are changed; other information in the diff / dump is preserved.
  • Display safehomes on the map. Active safehomes are displayed with greater opacity than inactive locations.
  • Change the status (active, inactive). If a previously unused item is enabled, an icon is placed on the centre of the map for positioning.
  • Clear (unset) one or all safehomes.
  • Upload and Download safehome and fwapproach data to/from the flight controller.
  • Manage INAV 7.1.0+ Autoland data

Clicking the "Edit" button at the end of row enables editing FWA parameters:

mwp safehome-edit

Note that editing functions are only available when the Safe Homes window is active; if the windows is dismissed with icons displayed, then the icons remain on the map, but are not editable.

Display safehomes at startup#

It also is possible to set a gsettings key to define a file of safehomes to load at startup, and optionally display (readonly) icons.

gsettings set org.stronnag.mwp load-safehome ~/.config/mwp/safehome.txt,Y

This sets the default safehomes file to ~/.config/mwp/safehome.txt and the appended ,Y means display the icons on the map.

If the file also contains fwapproach data, that will be applied as well.

If the name part is set to -FC-, then the safehomes will be loaded from the flight controller, for example:

gsettings get org.stronnag.mwp load-safehome
'-FC-,Y'

Example#

The image below shows a blackbox replay. Note that the flight home location (brown icon) is coincident with the pale orange safehome icon.

mwp safehomes replay

FW Approach (FWA) visualisation#

Please note that for the display of the geometry of the FWA, mwp uses the same rules as the flight controller; in particular the length of "base leg / dog leg" depends two CLI parameters, nav_fw_land_approach_length, nav_fw_loiter_radius. These are not part of the safe home (or mission) definition, rather they are properties of the model (and thus are persisted in a CLI diff file).

mwp can load these properties from a CLI diff/dump format file, as well as other CLI artefacts.

In particular, the length of the "base leg / dog leg" is the maximum of:

  • nav_fw_land_approach_length / 2 or
  • nav_fw_loiter_radius * 4

For example, in the first image the user had set nav_fw_land_approach_length to 150m (for a small, agile plane) but had accidentally left the nav_fw_loiter_radius at the default of 75m. The excessive radius dominates and gives an unacceptable geometry:

fwa1

Setting the radius to a more appropriate value for the model (40m) results in a much more acceptable geometry (still dominated by the loiter radius).

fwa2

In summary, in order to display FWA accurately for either safe homes or missions, it is advisable to provide a CLI diff format file containing at a minimum, set values for nav_fw_land_approach_length and nav_fw_loiter_radius. For the above example:

set nav_fw_loiter_radius = 4000
set nav_fw_land_approach_length = 15000