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

  • electrolics inc February 25, 2016 at 6:36am

    Hello,

    I am looking for some answers regarding altitude in mission planner.

    1. What does the 'altasl' (file attached) value stand for? is it the altitude of GPS only or does it represent Barometer only or mix of both?

    2. Where in mission planner (telemetry file) can I find altitude calculated from:

        i. GPS only

        ii. Barometer only

    I am using Pixhawk with 3.4.0 arduplane and misson planner 1.3.34.

    Please help me out understand and find the info I'm looking for.

    Thanks

    altasl.jpg

    https://storage.ning.com/topology/rest/1.0/file/get/3702192834?profile=original
    • electrolics inc > electrolics inc March 1, 2016 at 7:58am
      "Altasl" is 100% baro by default. And I've checked parameters the ALT_MIX is set to baro. When the plane moves/stays on ground over the span of minutes the "altasl" value jumps way high while alt stays almost the same. The plane flies OK and the pix hawk is working fine. I just can't understand this altasl and alt difference.
    • electrolics inc > electrolics inc March 1, 2016 at 6:04am
      Thanks, but that I know. What I meant to ask is that is this gps or baro reading, because "altasl" (100% baro) changes too much (1-9m) while on ground and alt reading remains almost same, very slight change (0.01- 0.10m) .
    • James Downing > electrolics inc March 1, 2016 at 6:12am

      Being that the barometer reading should be much more stable than the GPS altitude reading, it would lead me to believe that the stable one (ALT) is based on the barometer (or maybe mixed based on the parameter) and the jumpy one (altASL) would be GPS based.  But that's purely conjecture.

    • James Downing > electrolics inc February 25, 2016 at 6:54am

      That altitude is a list of where APM thinks it is.  It mixes this value from the baro and GPS based on the following parameter.  So - barometer - unless you've messed with this parameter.

      http://plane.ardupilot.com/wiki/arduplane-parameters/#gps_to_baro_m...

      I'm not sure where to find live raw GPS altitude data.  Might be able to read it in the log files.

    • electrolics inc > James Downing February 25, 2016 at 7:14pm

      ALT_MIX is default i.e 1 so this is showing 100% barometer,

      Does the mission planner show GPS alt under the status tab?

      I know I'll have dig into the dataflash log to find GPS alt, but playing back a telemetry log is easier in the mission planner GUI.

    • electrolics inc > electrolics inc February 29, 2016 at 11:48pm

      so what the value "alt" indicate under the status tab?

    • James Downing > electrolics inc March 1, 2016 at 5:33am

      I believe that is alt AGL, but I don't recall 100%.

  • James Downing January 29, 2016 at 8:31am

    Absolute = above sea level (ASL)

    Relative = above home altitude - the APM sets a reference altitude when it is turned on

    Terrain = above ground level (AGL) - the ground station references google terrain information

    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!

    Reference: http://plane.ardupilot.com/wiki/common-planning-a-mission-with-wayp...

    • Abolo > James Downing January 29, 2016 at 10:04am

      Good information James ,

      but I want to know if I use Absolute = above sea level (ASL)  should I but my waypoint alt in ASL ex: my ASL is 860 and my waypoint alt is 200 should I set it to  860 + 200 = 1060 ?

      3702614532?profile=originalhome alt (abs ) is ASL on Ground ? or Home point Alt AGL ?

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