Litchi ASL altitude data?

[marciano]

For years I've been using an app for programmed flights, iOS
It is still good but not updated for almost a year.
I bought Litchi a couple of years ago but used it only for tests.
I am planning to use it more frequently.
One data info that is very useful for me is the ASL (above see level) elevation of the selected point in the map.
Values are not exact but they bring a very good approach, specially where the ground has height variations of 20 or more meters.
I understand that those values are part of the map info. Google Maps has that info.
Is it possible to have them on each waypoint?
I also ask to display the scale of the map view at bottom.
Thank you

 

[Fly Dawg]

Values are not exact but they bring a very good approach, specially where the ground has height variations of 20 or more meters.

Litchi now has AGL references for each waypoint. ASL is not very useful, but AGL is.

 

[bsartist]

Litchi now has AGL references for each waypoint. ASL is not very useful, but AGL is.

Is AGL above the bottom of the body of water? Or might it know the water surface? I guess I should be able to test that out.

 

[Fly Dawg]

Or might it know the water surface?

Most every measurement I know of is above the water surface. Hence the term "Sea Level". AGL, one can safely assume would be the same. Assuming SL is considered zero altitude.

 

[bsartist]

Most every measurement I know of is above the water surface. Hence the term "Sea Level". AGL, one can safely assume would be the same. Assuming SL is considered zero altitude.

Sea Level is the nominal reference water level at the ocean level. This would not apply to lakes for example. So I fly over Lake George NY which has a nominal water surface of 300+ ft ASL. So I guess I need to test whether the AGL calculated in Litchi is above lake level or above the lake bottom.

 

[Fly Dawg]

So I guess I need to test whether the AGL calculated in Litchi is above lake level or above the lake bottom.

You shouldn't have to actually test this in a real time environment. Just create a simple "bogus" mission on the hub in AGL mode and note the difference between your set altitude and the AGL altitude that is noted. That should tell you.

 

[bsartist]

You shouldn't have to actually test this in a real time environment. Just create a simple "bogus" mission on the hub in AGL mode and note the difference between your set altitude and the AGL altitude that is noted. That should tell you.

Yes that’s exactly what I planned to do. I wasn’t planning on risking flying it below the surface if it actually follows the bottom terrain. LOL.

 

[Fly Dawg]

if it actually follows the bottom terrain. LOL.

LOL.....Yep..agreed....

 

[bsartist]

It indeed appears to consider the water surface ground level on Lake George. I programmed a mission over what I know to be significantly varying water depths and the AGL values for all those waypoints stayed the same. Except when a waypoint is over an island. Then it raises slightly.

I wonder what it does over locks. LOL.

 

[Fly Dawg]

I wonder what it does over locks. LOL.

One would think that it would consider the terrain parallel to the locks as opposed to the water levels. Not something that I have tried nor have any around to do so.....

 

[Meta4]

Sea Level is the nominal reference water level at the ocean level. This would not apply to lakes for example. So I fly over Lake George NY which has a nominal water surface of 300+ ft ASL. So I guess I need to test whether the AGL calculated in Litchi is above lake level or above the lake bottom.

Ordinary mapping doesn't show the bottom profile of lakes just as ordinary mapping doesn't show the bottom of the ocean.
You would need special purpose hydrographic charts to show underwater levels.

 

[bsartist]

Ok hopefully that wasn’t a hijack and we added some value to the OP’s question.

So bottom line is that I think Litchi will give you what you want with AGL being more useful as Fly Dawg pointed out. But you have to apply some good attention to detail.

You place your waypoints. Then select them all and then select that you want a certain height and then select above “ground.” It then recalculates all the waypoints altitudes. It will show you the height above ground and then, in parens, the height above or below the first waypoint (below in negative values such as with to take off on a mountain and fly down a valley.) I try to make my first waypoint at or very near my takeoff (home point).

Attention to detail comes into play in at least two ways. 1) it’s above ground level. Not above tree level. Add plenty to your waypoint heights to avoid obstacles. 2) the altitudes are only calculated at waypoints (I’m sure you know this ). So you need plenty if the terrain changes a lot to provide enough “sampling points” to avoid crashing into intervening bumps in terrain.

 

[bsartist]

One would think that it would consider the terrain parallel to the locks as opposed to the water levels. Not something that I have tried nor have any around to do so.....

I did. . Check it out.

 

[bsartist]

Ordinary mapping doesn't show the bottom profile of lakes just as ordinary mapping doesn't show the bottom of the ocean.
You would need special purpose hydrographic charts to show underwater levels.

That’s a good point. But I guess I don’t really know what counts as “ordinary mapping” and what Litchi may be using. I suppose it’s a bit much to assume they use bathymetric maps LOL. But I didn’t want to assume they don’t.

Even though Lake George, NY is not covered by official NOAA charts, I have several maps loaded into my pretty cheap MotionX-GPS app on my phone that have all bottom depths. So it’s not data that’s too far off the beaten path.

But this is me just defending my doubt. ;-). In the final analysis, you’re obviously correct.

 

[marciano]

Litchi now has AGL references for each waypoint. ASL is not very useful, but AGL is.

Planning a Waypoint mission do I have the AGL for each point?
If so it would be the ASL elevation of the point on the ground plus the planned flight altitude.
ASL is measured from a theorical shape of the Earth, like an spheroid.
In our matters (drone flights) the absolute ASL value might be useless unless we have to plan a flight far from our location and we need to evaluate atmospheric conditions, whatever.
Which is the height of Himalaya? 8800m ASL.
What is useful for me is the relative ASL elevation between two points. "Point A is 350m ASL, point B is 380m ASL". This indicates that if a would like to fly from A to B at the same AGL altitude (approx), I have to set a difference of 30m between both points.
ASL elevation is also useful looking for a good Home Point. Of course in relation to the way points.
And moreover, if you want to fly always at a fixed altitude you'll need all relative point elevations.

 

[Fly Dawg]

Planning a Waypoint mission do I have the AGL for each point?

Yes, if you read back in the previous posts you can simulate this with a non-active mission in the hub.

 

[marciano]

Yes, if you read back in the previous posts you can simulate this with a non-active mission in the hub.

I confess I assumed height I set to each waypoint is relative to the drone home point. Is that so?

 

[Fly Dawg]

I confess I assumed height I set to each waypoint is relative to the drone home point. Is that so?

This is correct, however, using AGL this accounts for terrain variations in the flight path and will maintain the aircraft at a particular altitude as the terrain altitude changes as opposed to maintaining a particular altitude AGL absolute.

 

[bsartist]

I confess I assumed height I set to each waypoint is relative to the drone home point. Is that so?

That would be correct BY DEFAULT. But Litchi added the capability to set height relative to ground. See my somewhat lengthy reply that I assume you haven’t read yet when posting this. Now you can select all waypoints and set height relative to ground.

As Fly Dawg implied several posts ago, you probably need to let go of your ASL mindset.

When you set all points relative to GROUND, they will be relative to the ground. Not SL. Not homepoint. When interpreting the number in parens then you need to understand that’s relative to first waypoint. I initially thought it was relative to homepoint but was shown that it was relative to first waypoint. But this number is in parentheses. It’s informstional if you will. The number outside the parens at each waypoint is the height above ground.

As FD also pointed out you can mess with this in the Litchi app or web based mission. Hub to prove this stuff to yourself. And I would say that’s a MUST for a Litchi beginner.

 

[marciano]

This is correct, however, using AGL this accounts for terrain variations in the flight path and will maintain the aircraft at a particular altitude as the terrain altitude changes as opposed to maintaining a particular altitude AGL absolute.

I understand. I see an "Above Ground" checkbox in hub waypoints. That's what I was asking for. It is not available in the app.
Thank you!
PS: there's also visible the scale rule