Welcome to PhantomPilots.com

Sign up for a weekly email of the latest drone news & information

Litchi altitude

Discussion in 'Pro/Adv Discussion' started by fortmed, Apr 27, 2016.

  1. fortmed

    Joined:
    Aug 8, 2013
    Messages:
    12
    Likes Received:
    0
    When instructions state waypoint height is relative to start height. What is met by this?


    Sent from my iPad using PhantomPilots mobile app
     
  2. alokbhargava

    Joined:
    Sep 28, 2015
    Messages:
    5,144
    Likes Received:
    1,659
    Location:
    San Francisco, CA
    This means all other waypoint altitudes are related to waypoint 1. If waypoint 2 altitude is 50', it means it it higher than waypoint 1 by 50'.

    And to be sure that you have enough clearance from ground, you should check the difference in elevations too and add heights of any obstructions like trees, buildings ....
     
  3. fortmed

    Joined:
    Aug 8, 2013
    Messages:
    12
    Likes Received:
    0
    So it is not related to starting program height but height of way point 1 only. So if waypoint 1 is 50 ft waypoint 2 is 50 ft it is the same height.


    Sent from my iPad using PhantomPilots mobile app
     
  4. Meta4

    Meta4 Moderator
    Staff Member

    Joined:
    Jan 8, 2014
    Messages:
    7,745
    Likes Received:
    3,457
    Litchi heights are exactly the same as in the DJI GO app.
    They are all relative to your home point which is zero.
    From Litchi waypoint help ...
    Altitude: The altitude of the waypoint relative to the elevation of the aircraft where it was powered on.
    See above. Waypoints are relative to home point - NOT to waypoint 1.
    If waypoint 2 is 50 metres, it's 50 metres above home point.
    Not at all ... that would be way too confusing and cause problems all the time.
     
    JTC likes this.
  5. fortmed

    Joined:
    Aug 8, 2013
    Messages:
    12
    Likes Received:
    0
    Thank you


    Sent from my iPad using PhantomPilots mobile app
     
  6. alokbhargava

    Joined:
    Sep 28, 2015
    Messages:
    5,144
    Likes Received:
    1,659
    Location:
    San Francisco, CA
    I always plan offline missions and Litchi references all other waypoints wrt to waypoint 1 as there is no home point. May be when waypoints are loaded to aircraft, they get readdressed but that doesn't affect mission. Not sure what happens if max altitude goes above the set limit.

    Thanks Meta4 for me to think again. I'm sure P3 will reference with reference to home point only.
     
  7. Ambivalent Squirrel

    Joined:
    Mar 29, 2016
    Messages:
    15
    Likes Received:
    2
    So, if you fly start on a cliff with a height of say 10m, the Phantom will maintain the same height if you go over the cliff? It won't descend to 10m above the beach?
     
  8. Meta4

    Meta4 Moderator
    Staff Member

    Joined:
    Jan 8, 2014
    Messages:
    7,745
    Likes Received:
    3,457
    Yes ... this gets asked a few times a week.
    Just like a plane or a helicopter, the Phantom won't plunge when it flies over a cliff.
    It will just keep flying - because your Phantom has no idea what is below it or how far below it is.
     
  9. Ambivalent Squirrel

    Joined:
    Mar 29, 2016
    Messages:
    15
    Likes Received:
    2
    thanks.
     
  10. Avocet

    Joined:
    Apr 3, 2016
    Messages:
    141
    Likes Received:
    36
    After taking off on said cliff, can you set a waypoint at an altitude 20 feet below the home point? (say there is a 100 foot drop off) .. .alt = -20 ??? The flight apps of other popular drones unfortunately assume the earth is FLAT.
     
  11. alokbhargava

    Joined:
    Sep 28, 2015
    Messages:
    5,144
    Likes Received:
    1,659
    Location:
    San Francisco, CA
    One should be careful in executing the mission as all altitudes will be referenced with respect to home point and if the home point is at lower altitude than waypoint 1, you may go totally wrong in estimating the heights of obstructions.

    I therefore keep my home point close to waypoint 1 or at least at the same level.
     
  12. matti

    Joined:
    Mar 15, 2016
    Messages:
    401
    Likes Received:
    62
    Thanks for the note ... I currently prepare my missions in Litchi mobile app. I wonder how that differs from "offline missions" done on a PC, then uploaded somewhere (...is there a potential point of failure if app A has different coordinates the app B expects when it then uploads mission info to the AC. i.e. what is the zero altitude: homepoint, waypoint 1, sea level or what??)?

    I have always prepared my Litchi missions assuming the altitude refers to the mission homepoint (i.e. the place where the AC is powered on).
     
  13. Meta4

    Meta4 Moderator
    Staff Member

    Joined:
    Jan 8, 2014
    Messages:
    7,745
    Likes Received:
    3,457
    The lowest setting Litchi Waypoint will allow is 5 metres above home point.
    If you want to fly waypoints lower than home point, you have to rethink the mission and launch from lower down.
    Home point will always be lower than Waypoint 1.
    You can't set a waypoint less than 5 metres above home.
     
  14. Meta4

    Meta4 Moderator
    Staff Member

    Joined:
    Jan 8, 2014
    Messages:
    7,745
    Likes Received:
    3,457
    When you are flying a Phantom, regardless of whatever app you use, the only height your Phantom knows is Home = zero.
    Every other height is relative to home.
    The Phantom has no idea where sea level is.
     
  15. Not A Speck Of Cereal

    Joined:
    Mar 8, 2016
    Messages:
    404
    Likes Received:
    145
    In response to Ambivalent Squirrel's questions in general (Litchi aside), if you start your HP (Home Point) at the top of a cliff, then fly over the cliff and descend, you will get a negative altitude number in the DJI Go app.

    It looks like folks are saying that the Litchi app won't allow that in respect to programming waypoints, but in general, that's what happens when flying: all altitudes are relative to the HP.

    Chris

    PS: Ambivalent Squirrel would make a good band name!
     
  16. alokbhargava

    Joined:
    Sep 28, 2015
    Messages:
    5,144
    Likes Received:
    1,659
    Location:
    San Francisco, CA
    I missed that Litchi allows waypoint_1 only if it's altitude is higher by min 5 m. Thanks for corrections. Good that Litchi has this protection built in.
     
    #16 alokbhargava, Apr 29, 2016
    Last edited: Apr 29, 2016
  17. alokbhargava

    Joined:
    Sep 28, 2015
    Messages:
    5,144
    Likes Received:
    1,659
    Location:
    San Francisco, CA
    Actually I wanted to stress on the point of elevations at every way point. Elevation of a waypoint is different than the altitude set for P3 to fly.

    If you work with mission hub for litchi and plan your mission there, you will see the elevation at each point and relative elevation with respect to waypoint 1. You can use the relative elevation to compute the ground clearance at each waypoint. This is very important if you are working on hilly area.
     
  18. Dadcat

    Joined:
    May 14, 2014
    Messages:
    224
    Likes Received:
    40
    Location:
    Portland Area, Oregon
    You can set a waypoint as low as 200 meters below the home point. Here's an example from iOS Litchi ver. 1.2.1 (I know it's old):

    image.png

    I just checked and the current Mission Hub will also allow negative 200m waypoints.

    I've never tried loading one like this onto the P3. It might not accept it, depending on firmware version.
     
  19. alokbhargava

    Joined:
    Sep 28, 2015
    Messages:
    5,144
    Likes Received:
    1,659
    Location:
    San Francisco, CA
    Thats what I thought works but picking lower altitudes is very risky as you need to check for elevations too at those points.
     
  20. Dadcat

    Joined:
    May 14, 2014
    Messages:
    224
    Likes Received:
    40
    Location:
    Portland Area, Oregon
    Absolutely. As you mentioned earlier, the Litchi Mission Hub helps you do that if you select "Map" and check the "Terrain" box.

    Another example for those who don't know about this:

    2016-04-29 (2).png