Litchi mission close call

Johnny21 · Mar 12, 2017

This is my first Litchi mission since my Phantom 3 Pro.I always use mission hub (PC version) to plan the mission and Google maps for elevations.Never had any problems.Today I started the mission and everything was going smooth until I saw my mavic heading to a tree.I hit pause and the mavic stopped just a couple of meters from disaster.I checked again the elevations and obviously they where wrong!
Conclusion:NEVER trust Google Maps for elevations,always double-check the terrain with your own eyes!

Skip near the end for the tree of terror!!!

cardplayer71 · Mar 12, 2017

Johnny21 said:
This is my first Litchi mission since my Phantom 3 Pro.I always use mission hub (PC version) to plan the mission and Google maps for elevations.Never had any problems.Today I started the mission and everything was going smooth until I saw my mavic heading to a tree.I hit pause and the mavic stopped just a couple of meters from disaster.I checked again the elevations and obviously they where wrong!
Conclusion:NEVER trust Google Maps for elevations,always double-check the terrain with your own eyes!

Skip near the end for the tree of terror!!!

It sounds like you know what you are doing, so forgive this amateur question. I have extensive experience with orienteering, not Litchi mission planning. Topographical maps list the elevation of the ground. Could this have been the problem, and you simply need to also account for the height of features, such as trees or structures? I agree that we always need to second-guess a data source, but Google Maps is not going to know the height of trees. My guess would be that they get their elevation data from USGS and other similar sources.

Regards,
cardplayer71

mmee · Mar 12, 2017

Wow! That was very close! Does obstacle avoidance work with Litchii?

MavicMo · Mar 12, 2017

I learned from my LHS to always survey the area I plan to shoot in person, before doing a Litchin Waypoint Mission. They told me a how they had planned a waypoint mission out in the plains which is relatively flat with no trees taller than maybe 60'. They had used google maps to check the area out.

When they got near the location they saw some huge rigs that were doing fracking. While they didn't know if it was in the direct flight path they were planning, but it was in the area with with structures a couple stories high...

I've gone a step further and try to fly the route manually to make sure there aren't any oddities or strangeness along the flight path...

integlikewhoa · Mar 12, 2017

I'm sure everyone know trees grow, and google maps don't tell you the tree height.

BorisTheSpider · Mar 12, 2017

Close one - glad your mavic survived it.

Were you using height above ground in Google earth when you exported the kml to import to the mission hub?

Also, can you remember how much terrain clearance you planned into the mission?

Kawboy12R · Mar 12, 2017

It'd be interesting to see the Litchi mission and where the waypoints were and the height above ground level listed. If I were planning a flight over that hill I'd have a waypoint on the very top as the best way to judge proper ground clearance rather than have ones farther down the hill and try to guess the clearance height. Also, pine trees "here" can often be 10m higher than normal tree height, so allowing 30m AGL won't clear a white pine, although the ones you almost hit weren't growing on the peak. I also wonder if the heights you were using managed to skip the peak contour line if it was just under the threshhold, so if they were say 10m resolution you might've been off as much as 9.x metres without seeing it?

boone · Mar 12, 2017

I watched that video and felt like I was watching a horror movie. Didn't know when the horrible thing was coming (seemed like there was more than one time it could have) but knew it was on the way, so I was stressed. Then when the moment was approaching, just like in a good horror flick, you could see it coming and you're all screaming at the screen, "it's right there! Oh my god, it's right there! Noooooo!".

Glad you saved it at the absolute last second there. Kudos. Spooky stuff.

Johnny21 · Mar 13, 2017

mmee said:
Wow! That was very close! Does obstacle avoidance work with Litchii?

No, I don't think so (mission)

Johnny21 · Mar 13, 2017

cardplayer71 said:
It sounds like you know what you are doing, so forgive this amateur question. I have extensive experience with orienteering, not Litchi mission planning. Topographical maps list the elevation of the ground. Could this have been the problem, and you simply need to also account for the height of features, such as trees or structures? I agree that we always need to second-guess a data source, but Google Maps is not going to know the height of trees. My guess would be that they get their elevation data from USGS and other similar sources.

Regards,
cardplayer71

I added 20 meters (about 60 feet) above ground level, so those trees should be cleared easily...

MrMavic · Mar 13, 2017

Johnny21 said:
This is my first Litchi mission since my Phantom 3 Pro.I always use mission hub (PC version) to plan the mission and Google maps for elevations.Never had any problems.Today I started the mission and everything was going smooth until I saw my mavic heading to a tree.I hit pause and the mavic stopped just a couple of meters from disaster.I checked again the elevations and obviously they where wrong!
Conclusion:NEVER trust Google Maps for elevations,always double-check the terrain with your own eyes!

Skip near the end for the tree of terror!!!

Google is weird when setting the elevation relative to ground in your path. When you enter, for instance, 60 meters on your first waypoint, then start making your path, it will re-set to "0" for some reason. You then have to set another waypoint and re-enter your elevation, then it will take. Just check it every time you start building the path for your mission. I have talked with others and it is that way for everyone for some reason. A Google Earth glitch that is just a little stubborn. I check it by habit now when I build the path. Hope this helps, and I'm glad you got her stopped in time. The forward sensors should have stopped it any way if you had them on.

Logger · Mar 13, 2017

Johnny21 said:
''I always use mission hub (PC version) to plan the mission and Google maps for elevations.

Did you remember to take into account any elevation difference between your Take Off point and Waypoint1?
If you forget this step and depart from a point that is 10m lower than the ground beneath WPT1 your entire route will be lowered by 10m regardless of what you have programmed. I expect you did not have this issue, but it something to consider.

Johnny21 · Mar 13, 2017

Logger said:
Did you remember to take into account any elevation difference between your Take Off point and Waypoint1?
If you forget this step and depart from a point that is 10m lower than the ground beneath WPT1 your entire route will be lowered by 10m regardless of what you have programmed. I expect you did not have this issue, but it something to consider.

This is my mission
Mission Hub - Litchi

Logger · Mar 13, 2017

The height on that mission looks like the should have worked.

I notice your POIs 5 and 6 are wrong though - not that this would have caused the collision. Having them set at 1m means the gimbal will point down an look at a postion inside the mountain 1m above your home take off point. You should really raise them to ~67m to equal the stated height above first waypoint.

Johnny21 · Mar 13, 2017

Logger said:
The height on that mission looks like the should have worked.

I notice your POIs 5 and 6 are wrong though - not that this would have caused the collision. Having them set at 1m means the gimbal will point down an look at a postion inside the mountain 1m above your home take off point. You should really raise them to ~67m to equal the stated height above first waypoint.

I did this because I wanted to "reveal" the city center while climping above the hill.

Logger · Mar 13, 2017

Ah I see. Makes sense. I assume your mission started right beside wpt1.

Jeremy · Mar 13, 2017

This is strange... I double check the ground elevation at waypoint 19 in Google Earth, your altitude should give you 53m clearance from the ground, excluding the trees, but those trees look 20m in height at most.

I also notice that in between waypoints 16 and 17, your Mavic is at about the same altitude as the road going uphill, which is 60m above the first waypoint, so your Mavic should be flying high enough at that point. I guess the elevation data for the very top bit of that hill is wrong. To me the hilltop is not merely 7m above the road, as seen from the Google map.

Logger · Mar 13, 2017

Seems the Google Earth terrain data is questionable here. Nothing beats doing a reccy flight to ascertain the true LSALT. Simple process, climb up while looking at highest point on proposed routes with gimbal level at 0 degrees. Keep climbing until you can see the horizon beyond it. If you can spin 360 degrees and all proposed obstacles lie beneath the distant horizon you are high Enough to clear them all. Note altitude and apply it to your Litchi route.

MavicFrank · Mar 13, 2017

Johnny21 said:
I added 20 meters (about 60 feet) above ground level, so those trees should be cleared easily...

Where trees are concerned I always provide at least 150 foot buffer AGL. Every crash I've had with my phantom has involved a tree so I'm not f'ing around with them any more.
I am really glad you had the wherewithal to be able to stop in time. Nice job. I would've needed a change of pants for sure.

Johnny21 · Mar 13, 2017

MavicFrank said:
Where trees are concerned I always provide at least 150 foot buffer AGL. Every crash I've had with my phantom has involved a tree so I'm not f'ing around with them any more.
I am really glad you had the wherewithal to be able to stop in time. Nice job. I would've needed a change of pants for sure.

Who said I didn't need new pants too?