Litchi mission height question

[Simmmo]

Hi can someone please tell me if I have got this right, am very new to this droning addiction.

I have a mission I want to fly that has very steep gradients, I am sure if I walked roughly to the middle of it I would be able to complete it to avoid maxing out at 120m which is much too low to get were I want to be. Using Google Earth I have the waypoint heights and they max out from bottom to top too early. So the question is if I set waypoint one to the middle can I send the Mavic from the end which is much lower and the Mavic will take its start height from waypoint 1 and not the much lower initial launch point which in turn will be the end point?

 

[lisadoc]

Litchi heights (altitude) are determined relative to your home point (not your first waypoint - unless they are one in the same). You need to position your home point to moderate your other heights relative to that position.

 

[JetexJim]

It is possible to reference waypoints to terrain height. see this video

 

[Simmmo]

It is possible to reference waypoints to terrain height. see this video

Hi thanks for both of your replies. I had already watched that excellent video and after doing a manual flight of the location and being unable to get high enough due to my location on that day I have done a mission utilising this feature. The feature highlights that I would have to be located roughly half way up the waterfall to avoid running out of height (waterfall is a cascade not a single drop). So to rephrase my question if I use the above method taking off say 40m in height below waypoint 1 and then send the Mavic to waypoint 1 will it start the mission as per the original plottings of 30m above ground for waypoint 1 that is relative to ground as per google earth file or will it be at -10m therefore crash into the hill side. I have plotted numerous waypoints to account for the steep terrain and they all show increasing height increments.
If it starts at waypoint 1 having been sent there from home location should it in theory complete the mission using all the predetermined relative to ground heights generated by Google Earth?

 

[53-63-6f-74-74]

For relative to ground missions -- Upon starting the mission the aircraft will move from wherever it is to way-point 1 in a straight line; It's not using your home point elevation for anything related to the mission. I usually take off first and manually fly somewhere close to way-point 1 (which is always close to me horizontally) before starting the mission to avoid any potential obstacles between take-off and mission start. I have also found it useful to to save my finalized Litchi mission as a CSV file and convert it back to a Google Earth KML, using Convert Litchi .csv file to .kml with elevation. You have to make sure your export from Litchi Mission Hub uses meters instead of feet, though. This will actually show your path in Google Earth with custom elevation changes that you have tweaked a little bit, such as if you wanted to fly relative to ground over some terrain for part of the mission but then descend down closer to ground level for a few way-points before returning to relative to ground heights.

 

[Simmmo]

For relative to ground missions -- Upon starting the mission the aircraft will move from wherever it is to way-point 1 in a straight line; It's not using your home point elevation for anything related to the mission. I usually take off first and manually fly somewhere close to way-point 1 (which is always close to me horizontally) before starting the mission to avoid any potential obstacles between take-off and mission start. I have also found it useful to to save my finalized Litchi mission as a CSV file and convert it back to a Google Earth KML, using Convert Litchi .csv file to .kml with elevation. You have to make sure your export from Litchi Mission Hub uses meters instead of feet, though. This will actually show your path in Google Earth with custom elevation changes that you have tweaked a little bit, such as if you wanted to fly relative to ground over some terrain for part of the mission but then descend down closer to ground level for a few way-points before returning to relative to ground heights.

Thanks for your reply, I am very inexperienced at this but am very impressed with Litchi waypoint missions having run one close to where I live a few times with very good repeatability (couple of noticeable glitches but overall very good, my failings didn't help).I am sure what you are saying is correct and in the next couple of weeks I will put it to the test and am sure it will be successful. Thank you. Though the excel stuff is a bit beyond my old brain at this time.

 

[dwallersv]

For relative to ground missions -- Upon starting the mission the aircraft will move from wherever it is to way-point 1 in a straight line; It's not using your home point elevation for anything related to the mission. I usually take off first and manually fly somewhere close to way-point 1 (which is always close to me horizontally) before starting the mission to avoid any potential obstacles between take-off and mission start.

Careful here, you're mistaken regarding how Litchi interprets waypoint altitudes. Relying on the description you give above will result in exactly the sort of accident @Simmmo has described if he flies the theoretical mission he proposes.

Litchi WP altitudes are always Home Point relative. This is because the aircraft has no idea how far above the ground it's flying over -- it only knows its absolute altitude relative to take-off. This is all Litchi has to work with.

Since no information on accurate HP altitude is available, Litchi has no way to correct for ground-relative altitudes.

All this is spelled out in the Litchi help.

However, there is an easy solution: Make your first WP the launch point. That way the first WP altitude will be correct ground-relative (it's the same as your HP), and the rest of the mission will work correctly.

Another way to do this is to launch from somewhere at the same altitude as the first WP, but I don't recommend this, as it's hard to ensure this. I suspect that that's what accidentally made your missions work, as you launched close to the first WP, and if not in a hilly area, you wouldn't notice the error.

 

[JetexJim]

Thanks for clarifying that dwallersv. I'd read the help but not soaked up that the altitude reference is relative to home point!

Additionally, the batch WP edit dialog, which seems to be the only way to select Height Relative to Ground, is then used to set several WPs to the same altitude.

I suspect that many users would prefer just to be able to set any WP altitude as altitude above ground. And, moreover, do it all at home using the Mission Hub. All this messing around on the tablet/phone at the launch site seems a bit odd but I suppose it's essential as the altitudes are/must be referenced to HOME POINT.

Regarding your suggestion of making the first WP the launch point - I take it that this entails making WP 1's altitude zero feet?

 

[53-63-6f-74-74]

There seems to be some misunderstanding. Certainly you can move ALL way-points to a relative to ground altitude regardless of your home point elevation or location. I've done it many times with my P3 and it works perfectly. You can do it either in the Litchi phone app by selecting all way-points in batch mode and just click "relative to ground" from the menu, or by using Google Earth on the PC, creating a relative to ground path using Google's elevation models, and importing the KML to mission hub. I prefer the latter because you can use GE in 3d view and account for quick terrain changes with more way-points. After moving ALL of them to the RTG elevation, you can then edit each individually up or down from that if you wish. Both procedures have nothing to do with the home point elevation, other than it being used as a 'reference' by Litchi, which is not clearly explained in the Litchi help, but means that even though the real-world elevation at the home point may be 1234, Litchi makes it 0000. Each way-point will still be a specified height over the ground directly below it (relative to 0000), within GE's terrain margin of error. That's why you need an internet connection to do this on your phone, because it accesses Google Earth's terrain model over the internet. There is no doubt, though, that your first way-point should always be very close to your launch point, and your last point should be as well.

 

[Chip D]

I did a flight a few weeks ago up a gorge, and in a relative short time I was up against the MAX 400' Elevation so I ended the flight and came back. I understand that the Litchi app looks at where I took off (AGL) and every waypoint is relative to that as far as elevation. I guess I could have somehow gotten to the top of the gorge and then flown to the bottom and then run my route and it wouldn't have been a problem.

My question is, what if I were to fly up to a place say 300' AGL, and then land. Then take off again and go up another 300' foot and then land. Now, wouldn't the MP have a new elevation registered. Of course this all assumes you can find a perfectly flat area to land multiple times.
Just wonderin'.

 

[53-63-6f-74-74]

I did a flight a few weeks ago up a gorge, and in a relative short time I was up against the MAX 400' Elevation so I ended the flight and came back. I understand that the Litchi app looks at where I took off (AGL) and every waypoint is relative to that as far as elevation. I guess I could have somehow gotten to the top of the gorge and then flown to the bottom and then run my route and it wouldn't have been a problem.

My question is, what if I were to fly up to a place say 300' AGL, and then land. Then take off again and go up another 300' foot and then land. Now, wouldn't the MP have a new elevation registered. Of course this all assumes you can find a perfectly flat area to land multiple times.
Just wonderin'.

I would think that you would have to be there and physically shut down and restart the aircraft in order to set a new home-point with an elevation of zero. Why not just raise your 400' restriction to the full 1640'? It applies to the ground under the aircraft, not your take-off elevation. Just batch set your way-points at no more than 400' relative to ground. The Litchi app will calculate and show the elevation of each way-point relative to your home point. If none are in excess of 1640 then everything is good.

 

[lisadoc]

I did a flight a few weeks ago up a gorge, and in a relative short time I was up against the MAX 400' Elevation so I ended the flight and came back.

I don't believe that you needed to do that. First of all, the 400-foot limit is not a law but guidance from the FAA, and is not a limitation posed by the DJI settings. Even if you consider the 400-foot limit manadatory, it is relative to ground height or an object (400 feet over a tall building for example), so you never would have violated that limit as long as you remained less than 400 feet above ground level at any point.

Additionally, DJI allows you to set maximum height of your MP at 500 meters, not feet (roughly 1,500 feet), so even if you're worried about conflicting with the DJI imposed height limit of 500 meters from the home point, you have plenty of elevation to play with. Correct me if I'm wrong here.

Also, as a side note, this is why I stick with earlier firmware and app versions, which allow me to change the height parameter limitations to well beyond 500 meters. As a result, no matter what the elevation change is, there is no need to consider the maximum change in elevations, since I wouldn't bump up against those restrictions.

 

[JetexJim]

There seems to be some misunderstanding. Certainly you can move ALL way-points to a relative to ground altitude regardless of your home point elevation or location. I've done it many times with my P3 and it works perfectly. You can do it either in the Litchi phone app by selecting all way-points in batch mode and just click "relative to ground" from the menu, or by using Google Earth on the PC, creating a relative to ground path using Google's elevation models, and importing the KML to mission hub. I prefer the latter because you can use GE in 3d view and account for quick terrain changes with more way-points. After moving ALL of them to the RTG elevation, you can then edit each individually up or down from that if you wish. Both procedures have nothing to do with the home point elevation, other than it being used as a 'reference' by Litchi, which is not clearly explained in the Litchi help, but means that even though the real-world elevation at the home point may be 1234, Litchi makes it 0000. Each way-point will still be a specified height over the ground directly below it (relative to 0000), within GE's terrain margin of error. That's why you need an internet connection to do this on your phone, because it accesses Google Earth's terrain model over the internet. There is no doubt, though, that your first way-point should always be very close to your launch point, and your last point should be as well.

I'd heard about using Google earth but it would make more sense just to be able to access terrain height from within the Litchi Mission Hub. Mission Hub loads a map with terrain data on it after all. However, that's probably a question for Litchi!

But regarding the use of Relative To Ground waypoint elevations. For me the matter making this difficult is that Mavic uses whatever the take off position as 0ft. This is hardboiled into the way Mavic functions and in truth what other altitude reference could it have except take off point?

But in the classic context of defining waypoints the actual Take Off position doesn't come into it. Of course, we, having gone through this discussion know now the difference between take off from the top of a cliff and take off from the bottom! But Litchi could make things clearer by emphasising how TO point influences all height references.

 

[Chip D]

I would think that you would have to be there and physically shut down and restart the aircraft in order to set a new home-point with an elevation of zero. Why not just raise your 400' restriction to the full 1640'? It applies to the ground under the aircraft, not your take-off elevation. Just batch set your way-points at no more than 400' relative to ground. The Litchi app will calculate and show the elevation of each way-point relative to your home point. If none are in excess of 1640 then everything is good.

Well all I know is that my Mission started out great on the Columbia River, and I started going up along the hills, and it came across on the screen that I was at my 400' height limit, and Litchi would go no further.
Chip D

 

[Chip D]

I don't believe that you needed to do that. First of all, the 400-foot limit is not a law but guidance from the FAA, and is not a limitation posed by the DJI settings. Even if you consider the 400-foot limit manadatory, it is relative to ground height or an object (400 feet over a tall building for example), so you never would have violated that limit as long as you remained less than 400 feet above ground level at any point.

Additionally, DJI allows you to set maximum height of your MP at 500 meters, not feet (roughly 1,500 feet), so even if you're worried about conflicting with the DJI imposed height limit of 500 meters from the home point, you have plenty of elevation to play with. Correct me if I'm wrong here.

Also, as a side note, this is why I stick with earlier firmware and app versions, which allow me to change the height parameter limitations to well beyond 500 meters. As a result, no matter what the elevation change is, there is no need to consider the maximum change in elevations, since I wouldn't bump up against those restrictions.

It's not the FAA, but the Litchi app wouldn't go higher.
Chip D

 

[53-63-6f-74-74]

I'd heard about using Google earth but it would make more sense just to be able to access terrain height from within the Litchi Mission Hub. Mission Hub loads a map with terrain data on it after all. However, that's probably a question for Litchi!

But regarding the use of Relative To Ground waypoint elevations. For me the matter making this difficult is that Mavic uses whatever the take off position as 0ft. This is hardboiled into the way Mavic functions and in truth what other altitude reference could it have except take off point?

But in the classic context of defining waypoints the actual Take Off position doesn't come into it but it's crucial. Of course, we, having gone through this discussion know now the difference between take off from the top of a cliff and take off from the bottom!

Mission Hub won't let you do very much as of yet (I hope this changes at some point); It does not have terrain data associated with it, only 2-d orthographic photos from Google Earth. The Mavic defines it's take off point as zero and Litchi defines subsequent way-point elevations relative to that based on the terrain model in Google Earth. So, your first way-point is set relative to the home-point zero. This is why your first way-point should be set to where you take off from. The Litchi app way-point bubbles will show the altitude of each point above the home point, and each way-point will be the altitude above Google Earth terrain that you have chosen. The easiest way to exemplify this is to create a mission and go through the process. Create a RTG mission in Litchi, export it to CSV and use the CSV to KML converting tool I linked to above. Open it in Google Earth and you'll see that it works (create the mission using metric data or it will not convert properly). That's half the fun as far as I'm concerned. I'll spend quite a bit of time planning and tweaking missions that I'll probably never fly any time soon.

 

[lisadoc]

It's not the FAA, but the Litchi app wouldn't go higher.
Chip D

Not sure I understand. Litchi doesn't limit me to 400 feet. Here's a screenshot of the Mission Hub, and as you can see, it allows me to set a waypoint at 1640 feet (500 meters).



How are you being limited to 400 feet?

 

[Chip D]

Not sure I understand. Litchi doesn't limit me to 400 feet. Here's a screenshot of the Mission Hub, and as you can see, it allows me to set a waypoint at 1640 feet (500 meters).

View attachment 22406

How are you being limited to 400 feet?

I was doing the flight and watching my Iphone, and it stopped and said 400' Max or something like that. Dunno anything more than that. So I brought it back and gave up.

 

[53-63-6f-74-74]

I was doing the flight and watching my Iphone, and it stopped and said 400' Max or something like that. Dunno anything more than that. So I brought it back and gave up.

Is your max altitude in DJIgo set to 400'? That might be your problem. Litchi uses the DJI SDK. Some aircraft settings MUST be made in DJIgo to be effective in Litchi.

 

[lisadoc]

Is your max altitude in DJIgo set to 400'? That might be your problem. Litchi uses the DJI SDK. Some aircraft settings MUST be made in DJIgo to be effective in Litchi.

That would be my guess too.