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Litchi - Google Earth Notes

Discussion in 'Control (Go, Litchi, etc..)' started by Avocet, Aug 25, 2016.

  1. Avocet

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    For those interested in refining the usage of Google Earth imports into Litchi, I just wanted to pass along something I've discovered with the hopes its useful to others. Perhaps some of you may have figured this out already, and I apologize for the redundancy.

    There have been several posts and videos in most of the Phantom forums about using the Path tool in GE to take advantage of the GIS terrain data which will automatically provide altitude changes (AGL - above ground level - ready for 107?) over a given path - in our case a flight path for waypoint mission creation.

    [We create a path in GE, save the path as a KML file and import into Mission Hub at flylitchi.com.]

    Here's what I have discovered:

    1. Let's say you create a path with a 10m buffer from the ground and your path is "relatIve to the ground" in GE. If your path STARTS (this will be Waypoint 1) at the lowest point and your next series of paths will realize INCREASES in altitude above the ground, the Litchi mission import will do a nice job of setting the waypoints with increases in altitude for each of the waypoints. Fine.

    HOWEVER,

    2. If your path STARTS (WP#1) at the HIGHEST point of your mission plan and places path points over terrain that is DECREASING, or terrain that is lower or falling away from the starting point altitude, then, after importing that KML file into Litchi Hub, all of the waypoints altitudes will be what you entered into the starting altitude in your GE path screen. Litchi will show the elevation from starting point as XXm BELOW starting point. The elevation at all Waypoints will remain constant/unchanged if the ground level elevations are less than the ground elevation at WP#1 (mission start).

    This is difficult to convey in words - I suggest you try two short paths in GE. The first ascending over rising terrain and the second descending over the same path. Import both of them into the Litchi Hub and see how the hub sets up the waypoint elevations and the elevations from one waypoint to the next.

    On the waypoint information screens in Litchi (select an existing waypoint), buried and sitting very quietly under "Altitude" is some dynamic text: "Ground Elevation: 1m (0m below first waypoint)". This string of text will be critical to study if your mission plan descends over lowering terrain.

    Sorry to blab on ... this was a moment of important clarity for me. Thought I'd share for those who value their UAV experiences. Way too many folks overlook altitude in their missions and are crashing into terrain or terrain features. Litchi cannot account for anything that rises off the surface of the earth - trees, buildings, neighbors, neighbors friends, etc.
     
  2. matti

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    Hmm. I tried it and the AGL vs ground elevation seemed to be correctly in sync both ways (I used Google Earth Pro and Safari in OS X 10.11, if that matters).

    When going up, the AGL increased from 30m to 62m because ground elevation was 32m.

    When going down, the AGL decreased from 30m to -2m because ground elevation was -32m.

    This was very handy because those calculations were done automatically. With Litchi Mission Hub-only I must always do that error-prone AGL + ground elevation calculation myself to each waypoint (or am I missing something?).
     
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  3. Avocet

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    Hmmm ... what I have found has to do with the starting point of your path in GE. If you start your path and create it while ascending, the import into Litchi Hub shows altitude that ascends as you might expect.

    If, however you start your path say on top of a hill and make the path down hill, the imported waypoints all stay at your WP#1 altitude which was set in the GE path interface.

    Does that make sense?
     
  4. matti

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    I tried this again and it didn't matter whether the path was ascending or descending. In both cases the altitude set in GE varied in the Litchi Mission Hub depending on the ground elevation so the AC was always in the same height from the ground. So it works as expected.

    I wish Litchi Mission Hub worked like that, too, without a detour to GE.

    I noticed that If I left GE altitude at its 0m default, then Litchi Mission Hub used its default altitude instead.
     
  5. STAINLESS

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    OP's issue can be replicated by leaving altitude "Clamped to the Ground"
     
  6. GMack

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    I made a GIF that shows the issue under the Drone rescue thread where a drone hit a mountain. See this post and item #6 and watch the red arrow: Drone rescue?

    AutoPilot is also aware of this Google Earth import mission issue too. Their suggestion was to fly the route and use the "Use current location as a waypoint" marker. They may try and do a side view of the flight to show the proposed mission/flight path (If Google Earth will lie flat!), or show that altitude changing as seen from above in their little moving drone icon during planning to show if the craft is ascending or descending over the route soon enough to clear things under it.

    Be careful in planning near tall items with GE. Flight could be risky!
     
  7. BigAl07

    BigAl07 Moderator
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    Is there a video tutorial on how to incorporate GE into Litchi? I love the idea of using this along with Mission Hub but have no clue where to start.
     
  8. CRF319

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  9. matti

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    Google Earth path to Litchi Mission Hub:

    Google Earth > Add > Path > Left-click a path > Altitude tab > Relative to ground, set desired AGL Altitude for the AC (with 0m Litchi Mission Hub defaults to 30m AGL) > OK
    > File > Save > Save Place As... > Kml

    Litchi Mission Hub > MISSIONS > Import > Choose File > Import to new mission

    Ground elevations are automatically added to the desired AGL.

    Drawing paths and polygons - Earth Help

    [edit: CRF319 ninja'd me by 2minutes so I deleted duplicate Youtube links]

    ...I've heard rumors that Litchi has a beta version which makes this detour to Google Earth unnecessary.
     
  10. GMack

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    Heed the words at the end of the forest video where he says: "Use with caution!" Flight plan may not be what it appears to be in very tall surroundings, imhe.

    Fwiw, AutoPilot's support used the word "Risky" with me due to variables like rate of climb, barometer, wind, bad GE output in planning stage (i.e GIF mission from GE mentioned above that shows clear sailing over the mountain, but obviously it isn't.), air density, faulty initial altitude when turned on, etc. I'm waiting to see how they handle this in an update as one could fly into a mountain side if not careful in planning.
     
  11. BigAl07

    BigAl07 Moderator
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    Thanks gang. Now I'm armed with information and desire to push the limits :)
     
  12. matti

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    Make sure that there are no unexpected ground elevations between waypoints. You can inspect the whole path in Google Earth by ctrl-clicking the path (in Places at center left) and choose "Show Elevation Profile". Or just move the cursor on the map and check the "elev" figure at lower right.

    And do leave some margin for error because I guess Google's ground elevation info might not always be very reliable.
     
  13. Avocet

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    Yes to all of the above. Here, again is the GRAY AREA. Published Phantom 3 Pro/Adv specs show the climb rate to be 5 meters per second climb and 3 m/s descent. This is corporate communication. There are many variables that will make that statement quite inaccurate - wind, heat, humidity, density air, aircraft performance, etc. As such, proceed with extra EXTRA caution and planning.

    Some have designed Litchi missions that have sped into obstacles like trees or rising terrain because the craft could not ascend quickly enough to make the assigned altitude arriving at the waypoint. Use interim waypoints and step up your way to altitude in increments if you are unsure of the terrain changes of ascent.
     
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