Does someone know and can share what the difference is between the Altitude settings in Mission Planner for Relative, Absolute and Terrain. I know that the Terrain is for those planes equipped for terrain following, but what about the other 2 settings?  I have had some problems with my X-8 wing holding requested altitude and suspect this might be the problem. HELP and thanks!

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Absolute Altitude pertains to altitude above sea level.

Relative Altitude pertains to altitude above home/launch position.

If you are flying over hills or over other areas with varying terrain that increases or decreases that you use the "Verify Height" option in MP. This will allow MP to adjust the waypoint altitude in order to keep your X-8 at the desired altitude.

Todd H.

I know that in Mission Planner there is a verify height check box.  If it is checked it will adjust the way points so that the height of the mission will match the height of the ground at that location.  So if your default height is 20 Meters and the ground is 10 Meters above Home then it will make a way point height of 30 Meters.

This is based on Google map data and where you have home defined at the time.  Otherwise all heights are relative to where you take off from.


thank you--thanks makes sense!

thanks --that answers a lot of questions I had!

Do 'Terrain' waypoints do the same as the 'verify height' checkbox, if not what's the difference?

Verify Height only applies to each waypoint. Terrain Following will continuously adjust the altitude between waypoints. Verify Height will not adjust for a hill between two waypoints, unless you place another WP on top of the hill.

I believe that it has been reported before that the "verify Height" function is not a continuous second by second check and adjustment.  It is rather something that happens periodically and if I remember what was reported it may be at 100 meter intervals.

So it could still be possible to have trouble in rapidly rising terrain if cutting it to close.

Thanks, that makes things clearer.

It's interesting that there is a "Absolute Altitude" vice "Means Sea Level or MSL" and a "Relative Altitude" vice "Above Ground Level od AGL".  Shouldn't everything be referenced in mission planning as it is in the aviation community as a whole?

In addition to this, I think a sonar, lidar, or something equivalent is used to terrain following directly below the aircraft.  The idea of have it in the flight computer would be nice but I do not think current designs have the robustness to be able to hold all the DTED (Digital Terrain Elevation Data) it would take to be able for the air vehicle to fly truly autonomously.  Therefore, it makes sense to use waypoints AGL and fly in Auto if you plan to fly along diverse terrains. 

Terrain Following came out in 3.1 and uses the CF card to store the terrain data.

The reason we don't use the term AGL is because it is not accurate. We use "Relative" because it is relative to launch elevation, not all the ground.
I agree that MSL would be a more aviation friendly term than Absolute, which is more of a cartography term.

Note that according to this:

terrain following applies only to arduplane, not copters yet. So don’t count on this feature for automatically adjusting your altitude if you fly a copter. 

I think maybe there is some confusion about what was discussed above.  It was not "Terrain following" but rather the "verify height" check box on the waypoint menu of mission planner.

"Verify height means that the Mission Planner will use Google Earth topology data to adjust your desired altitude at each waypoint to reflect the height of the ground beneath. So if your waypoint is on a hill, if this option is selected the Mission Planner will increase your ALT setting by the height of the hill. This is a good way to make sure you don’t crash into mountains!"


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