What different between ( Absolute , Relative , Terrain ) Alt in MP ?

Posted by Abolo on January 29, 2016 at 8:02am

Hi again ,

I am still having problem in Auto modes using Pixhack FC

My Question is

What's the different between ( Absolute , Relative , Terrain ) Altitude in Mission planner ?

Whats is the function of the check box ( verify Height ) ?

also in the right side under Home Location there are

Lat : -------------

Long : ------------

Alt (abs ) :-----------

Dose Alt (abs ) effect the flight altitude ?

Why always altitude keep drop in auto mode ?

this is my screen captured for the mission planner  , flight plane Tab

dose there any problem in my MP version,?

3691271162?profile=originalhope I can figure out any useful information ,,

regards ..

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Replies

    • James Downing > Abolo January 29, 2016 at 10:56am

      Another thought - could your barometer be misreading your altitude?  Do you have an OSD?  When you get into the air and flying, does your OSD report your altitude correctly?

      I'm wondering if you may have an air vent in the wrong place that is pulling negative pressure in your aircraft fuselage and affecting your APM's ability to read altitude.

    • Abolo > James Downing January 30, 2016 at 12:03pm

      My OSD looks reading the altitude correctly from the ground as I also test it in ground with also my Garmin watch ,

      dose there any way to test barometer ?

      am interesting in know if I have air vent in fuselage , how ? can you provide me with any information or source guide .?

      A lot of thanks James .

    • James Downing > Abolo January 31, 2016 at 5:13pm
      Just fly it and see if it's reporting 60m altitude when it appears 60m high. See if it reports 10m when it appears 10m high.

      The fuse vent was just a thought. Flowing air can create vacuums or can create stagnaton pressures that I've always thought could mess with barometers snice they are so sensitive. I've never had an issue, but it's a possibility I guess. Otherwise I'm kinda out of thoughts unless your waypoints are just being input incorrectly.
    • Moderator
      Dwgsparky > James Downing February 27, 2016 at 3:19pm

      I had a similar problem with a flying wing with the pixhawk built into the wing, I solved it by making a 3/16 hole through the wing near the pixhawk to allow the pressure to average between the top of the wing and the bottom of the wing. works great. 

    • Abolo > James Downing February 1, 2016 at 6:49am

      thankx James ,

      I will try that test in next fly ,

      Dose there any way to test all sensors in the ground ? 

      just like simulation ( I couldn't connect the FlightGear to Mission planner until know )

      regards ,

    • James Downing > Abolo February 1, 2016 at 10:26am

      I don't know of a way to click a button and test everything.  You can test each one individually for proper response to an input though, depending on what they are.

      For instance, a barometer reacts to air pressure.  You can set a GPS home point, then drive up or down a big hill and see if it responds appropriately.

      The issue I brought up is a dynamic test that requires airflow over your fuselage to really test how the airflow is affecting air pressure in your fuselage.  The only thought I have there is to strap the fuselage to the outside of your car and go for a drive.  It seems like a good way to damage your fuselage though.

    • Abolo > James Downing February 1, 2016 at 11:02am

      nice way ,

       The Car roof alt about 2 meter, Is it enough for Auto mode to work in speed about 60 kph ?

      what about simulation flight gear dose it simulate all sensor ?

      kindly visit this link

      Mission planner simulation with FlightGear for ( Plane ) fails.

      all regards ,

    • James Downing > Abolo January 29, 2016 at 10:40am

      I've only worked in relative mode.  To me, absolute settings are a good way to mess something up.

      Home altitude should be the ground altitude ASL.  Your RTL altitude is set above the home point in a separate parameter which sets it AGL.

  • Roger Monongo January 29, 2016 at 8:22am

    Absolute altitude is the altitude given by the GPS above the reference ellipsoid of the GPS constelation, the WGS84.
    Relative altitude is the height relative to the plane/copter's initial position.
    Terrain altitude I guess it's the altitude above the terrain model as is in the ground station.

    I wonder if there is the possibility to import to groundstation the geoid undulation model so one could calculate instantly and accurately the orthometric altitude, i.e. the altitude above mean sea level. That would be very interesting.

    • Lee Kelley > Roger Monongo January 29, 2016 at 8:28am

      So, I've typically used relative altitude, because that's what is the most straight-forward for my brain, but it's surprising that there's not a way to just use good ol' MSL.  As a pilot, I would appreciate using MSL.   

      So, is Terrain Altitude only usable if the plane is connected via Mavlink?  How would it get the terrain altitude in real time?

      Thanks for your help, by the way!

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