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Litchi Waypoints and height AGL

Discussion in 'Pro/Adv Discussion' started by MILLER4PRESIDENT2020, May 20, 2016.

  1. MILLER4PRESIDENT2020

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    Litchi waypoints are great but I haven't gone out of site or had a significant change in altitude yet. If I plot a course and set the altitude as 200 feet for each waypoint, is it going to maintain 200 AGL throughout the entire course? Like if I have a course around a mountain is it going to crash itself into the side of the mountain? PLotting the course online you can see that it knows ground elevation is 3013 feet which is 1543 above the first waypoint. It would appear the Litchi is smart enough?
    upload_2016-5-20_15-35-53.png

    But if Litch is smart enough and it goes by AGl how does it react in the following situations:
    - What if i plotted a course across the Grand Canyon at 100 feet from one rim down to the other and their was a waypoint in the middle? Is the bird going to start descending once it goes over the edge and then climb to clear on the other side?
    - What happens if I launch from the top of the mountain which is about 3000 feet and fly straight out for a few miles. What happens when the ground underneath me is now a few hundred feet MSL, meaning I have exceeded the 500 M altitude height restiction? Is this sort of a work around to the 500m restriction because it is based on where your home point is logged? So if you start in a higher spot then you can actually go higher than if you started at sea level? This must be the case because then how do people in Denver fly?
    - What about the opposite? If I start at sea level and plot a course up a mountain that is 2000m high. Is it going to start out up the mountain until it hits 500m and stop climbing even though I am still only 200 feet above the trees?

    Thanks
     
  2. jonebk12

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    You will crash into the mountain in your first example. Litchi waypoint altitudes are all relative to your takeoff point/altitude. If you set a waypoint 200 feet up, 500 feet away, the quad will fly to 200 feet above your takeoff point. It doesn't know/care what's underneath it. DO NOT fly that mission if the elevation of the ground underneath any of those waypoints is in fact 1500 feet higher than where you're taking off from.
     
  3. Wolfiesden

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    Every app for the phantom (that I know of) operates on relative altitudes. That being relative to your TAKEOFF altitude. None actually look at topo data and maintain true AGL during flight.

    For example, (if you could fly in the grand canyon which you can't due to it being a national park) taking off from the rim of the grand canyon to 100' and flying out over the canyon, is technically against FAA rules as they are currently written. Once you fly out off the cliff edge, you will likely exceed 400' AGL at that point but the phantom and its tracking data will say it was at 100' despite it being 2000' above canyon floor.
     
  4. MILLER4PRESIDENT2020

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    No worries I am not about to jump into it that deep. I have been slowly go further and further observing what happens. I was just using that as an extreme example
     
  5. n6vmo

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    If you look at the data for Way Point 5, I have it circled. It say that Way Point 5 is 1543' above your first way point. In order to clear the obstacle, you will have to set WP#5 to 1543' + 200' or 1743'. That will have the P3 fly 200' over WP#5.

    2.jpg
     
  6. jonebk12

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    The other thing to consider is that when flying Litchi mission with waypoints set to different altitudes, the quad gradually rises (or descends) between waypoints. So if you were to take off from the floor of the Grand Canyon and set your first waypoint 100 feet above you, and then set the second one somewhere outside of the rim, even if you take into account the elevation change, the quad will not consider the topography between waypoints. You would likely crash into the wall.
     
  7. alokbhargava

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    All attitudes are referenced to the home point and thus Litchi will not check the elevation of each waypoint wrt sea level and adjust the altitude automatically. If you are in an unknown territory you should plan your mission using mission hubs on flyLitchi.com on a big tablet. That shows elevation of every point.
     
  8. MILLER4PRESIDENT2020

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    Thanks guys. I went out to a big hill today in the woods and started messing around with waypoint heights. It is making sense now. Still not confident enough to send it out of sight or up a mountain.....maybe someday!
     
  9. DronePI

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    If you want some really good instruction for minimal cost, you should check out Phantom Filmschool offered at Phantom Filmschool - the easy way to shoot like a pro!
    I've never been one to pay for courses like this with all the tutorials available online but I will honestly say there is nothing like this if you want to know how to use Litchi and take great shots. It's all in one place, very thorough, and very convenient. Well worth the small cost! Just FYI
     
  10. MILLER4PRESIDENT2020

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    I checked it out briefly and it seemed more like how to film like a professional. Like how to get interesting camera angles and stuff. I know how to do that. I am more interested in the technical aspect of Litchi. I could be wrong though and maybe I didnt delve deep enough into phantom film school. But that was my impression from the quick intro.
     
  11. kenargo

    Approved Vendor

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    Ultimate Flight can use either AGL or ATO. A mission can be configured using above ground level and UF will calculate the ATO (which the mission needs). I have many users who require similar for various measurement missions and they user mission templates and/or fixed AGL altitudes and allow the app to calculate. In addition UF supports digital terrain models (which are highly accurate ground elevation maps). DTM can be downloaded from various sources and are significantly more accurate than the elevations returned by Google Elevation.

    In short, there are 2 ways to solve the AGL missions, both built into UF.
     
  12. Wolfiesden

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    Thank you. I have not seen or used UF. Nice to know that an app exists that takes ground contour into account.
     
  13. matti

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    In my limited experience it seems Litchi will slow down the planned horizontal speed so the AC has enough time time to climb over an obstacle if the next waypoint is directly above the obstacle (NOT after the obstacle).

    I have only tried this while descending: I had max horizontal speed 54km/h with waypoint #4 at 110m altitude and waypoint #5 at 20m altitude -- the horizontal distance from #4 to #5 was just 50m. The AC did seem to clearly slow down its horizontal speed to it had enough time to descend those 90m. I believe this would work in the opposite direction, too?

    I haven't yet tried Litchi mission hub. How accurate are those Google Maps elevation figures when climbing up a hill? I guess it is best to run a slow test mission with plenty of safety margin first?
     
  14. n6vmo

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    Yes, that is what Litchi does. It will maintain the 3D path by slowing down horizontal speed to reach a programmed altitude.

    You can see this happen in the video below. Fast forward to the 7:00 mark. You will see the mission speed is 12MPH. Then the program needs to negotiate over some power lines over a short distance. The horizontal speed slows to around 7MPH so the P3 can get to the programmed altitude. Then once it reaches that altitude, it then increases horizontal speed back to 12MPH.

    The mission profile is the link below. The change in altitude was from W#10 to WP#11



    http://www.phantompilots.com/attachments/litchi-flight-jpg.52519/
     
    #14 n6vmo, May 23, 2016
    Last edited: May 23, 2016
  15. kenargo

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    This is a firmware behavior, not app specific (all apps will act the same as waypoint operations are firmware).