Litchi - Using online elevation and DEM

[TheDigitalDove]

i am not having success with online elevation in litchi waypoint mission
i am trying to do low elevation flights skimming the ocean and surrounding rocks and beach
if i take off at close to sea level it all words out, but i cant always do so due to cliffs and access

1) what is the procedure for setting onlinve elevation. i enable it in mission hub settings and i click above ground on each waypoint - is this correct?
Because it has little impact on my flight which generally seems to still fly at that set elevation Above my taken of elevation. of waypoint 1. If i dont take off at the same location and elevation its a mess using the waypoint 1 method.

2) This is at Bondi in Sydney in Australia - and i assume the elevation data is available but is there someway in litchi hub of knowing if this is available and being used.?
In some cases i have visually watched from the cliff and then set the negative elevation value, but off course if i then cant rely on elevation dat and take off from a lower location it is likely to drop into the ocean ( but for possible obstacle avodance)

3) if i go down the route of ex[;promg DEM files is this a more accurate and possibly successful alternative

 

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

There is a check box in the online mission hub settings to "use online elevations" and also a second check box for each waypoint under the altitude slider. Both must be checked. You may also batch select several or all points using control and left click to do all of them at the same time. You will then have two different elevations shown at each waypoint. One will be elev above takeoff, the other above ground. They should be different, except for waypoint 1. DEM files need to be WGS-84 Esri ASCII Grid and if you don't have knowledge of how to convert formats then you will have difficulty, and it is difficult to determine accuracy of publicly available DEMs. You should always leave a significant buffer. I just made a test mission in Bondi and it is working fine for me. Post a link to your mission here if you are still having problems.

 

[sar104]

i am not having success with online elevation in litchi waypoint mission
i am trying to do low elevation flights skimming the ocean and surrounding rocks and beach
if i take off at close to sea level it all words out, but i cant always do so due to cliffs and access

1) what is the procedure for setting onlinve elevation. i enable it in mission hub settings and i click above ground on each waypoint - is this correct?
Because it has little impact on my flight which generally seems to still fly at that set elevation Above my taken of elevation. of waypoint 1. If i dont take off at the same location and elevation its a mess using the waypoint 1 method.

2) This is at Bondi in Sydney in Australia - and i assume the elevation data is available but is there someway in litchi hub of knowing if this is available and being used.?
In some cases i have visually watched from the cliff and then set the negative elevation value, but off course if i then cant rely on elevation dat and take off from a lower location it is likely to drop into the ocean ( but for possible obstacle avodance)

3) if i go down the route of ex[;promg DEM files is this a more accurate and possibly successful alternative

This is a common issue that is not well addressed in the Litchi documentation. The AGL feature in Litchi works fine, but the essential point to remember is that the altitudes that result in the uploaded mission profile are still defined relative to an initial reference takeoff elevation. In other words even though Litchi references the waypoint altitudes relative to ground, the mission profile ends up defining the waypoints in reference to altitude zero, which is the takeoff elevation.

As a result you always need to have the first waypoint altitude referenced to the takeoff point. If the first waypoint is not directly above the takeoff point then it must be set relative to takeoff, not as AGL, while if it is directly above the takeoff point then AGL and relative altitude are the same, so either will work. Either of those approaches then correctly references all subsequent altitudes to the relative altitude that is all the aircraft cares about.

 

[theDRONEranger]

sar104 gave good advice for the LITCHI program. Not settings the altitude waypoints correctly can have dire results.

Just spent 3 wonderful, glorious weeks at WSMR. Not a place a place I like to get called to, especially over the holidays.

 

[sar104]

sar104 gave good advice for the LITCHI program. Not settings the altitude waypoints correctly can have dire results.

Just spent 3 wonderful, glorious weeks at WSMR. Not a place a place I like to get called to, especially over the holidays.

At least it's not summer.

 

[theDRONEranger]

At least it's not summer.

Not a hunter, I follow Buddhism, but if I were, the Oryx I saw would most likely be a very fitting meal.

 

[sar104]

Not a hunter, I follow Buddhism, but if I were, the Oryx I saw would most likely be a very fitting meal.

I know a few hunters here who have bagged Oryx and I can confirm that they make very tasty stew and burritos. I couldn't shoot one either though. I'm much happier knowing that I get meat from animals that died from natural causes before appearing on the supermarket shelves.

 

[theDRONEranger]

And that is exactly how I get mine. Their hearts finally stopped pumping, amazingly right at the butcher shop. It’s acceptable as long as I not the one to take the life.

Don’t get me wrong, I love the 2nd and I do own guns and possess a National Concealed Carry (valid in all 50+DC). I will protect with extreme prejudice.

 

[TheDigitalDove]

There is a check box in the online mission hub settings to "use online elevations" and also a second check box for each waypoint under the altitude slider. Both must be checked. You may also batch select several or all points using control and left click to do all of them at the same time. You will then have two different elevations shown at each waypoint. One will be elev above takeoff, the other above ground. They should be different, except for waypoint 1. DEM files need to be WGS-84 Esri ASCII Grid and if you don't have knowledge of how to convert formats then you will have difficulty, and it is difficult to determine accuracy of publicly available DEMs. You should always leave a significant buffer. I just made a test mission in Bondi and it is working fine for me. Post a link to your mission here if you are still having problems.

thanks, i have set both of those yet it still doesn't find elevation above sea level and rather elevation above my takeoff point. As a bond local you will understand that i am trying to approach ben buckler from north side below cliff level , rise over the headland drop over the other side and yes i just don't have the confidence to test my current flight path by taking off at sea level given it was set atop the cliff some 30 metres above sea level . i will post flight path .

i have tried extensive alternative flights simply following the curve of the beach out at sea and each time it shoots based on my take off elevation. Again yes i have set both your settings and i am familiar with the annotations and color coding of the two elevations at the waypoint.

i guess making a short story long - file to be posted for consideration

 

[TheDigitalDove]

This is a common issue that is not well addressed in the Litchi documentation. The AGL feature in Litchi works fine, but the essential point to remember is that the altitudes that result in the uploaded mission profile are still defined relative to an initial reference takeoff elevation. In other words even though Litchi references the waypoint altitudes relative to ground, the mission profile ends up defining the waypoints in reference to altitude zero, which is the takeoff elevation.

As a result you always need to have the first waypoint altitude referenced to the takeoff point. If the first waypoint is not directly above the takeoff point then it must be set relative to takeoff, not as AGL, while if it is directly above the takeoff point then AGL and relative altitude are the same, so either will work. Either of those approaches then correctly references all subsequent altitudes to the relative altitude that is all the aircraft cares about.

Yes given circumstance i can get down with aircraft to set my first waypoint at almost sea level take off and then set all from there. OR as i had hoped do it all in mission hub correctly and it would fly it regardless of take off point not being at waypoint 1.
BECAUSE for executing the full mission safely, I need re-locate myself and TAKE OFF from a 25m higher elevation and not above waypoint 1. This jacks the whole mission up 30m and throws off all POI focus points

If i understand your comments correctly:
1) i should make calculations based on my takeoff position being x-metres higher than take off at waypoint 1 and then
2) set negative elevations for each waypoint to correct for this and so set my desired flight altitude and it will replicate the flight i had intended


But I was hoping to:
1) USE online elevation data, create in mission hub as it has data to provide elevation above sea, ground or a structure and fly the waypoints based on clearing those elevations regardless of take off location

2) OR.... alternatively after setting waypoint 1 using the aircraft position live and not mission hub to visually assure my clearance of all items on the flight path , i could then relocate to higher ground and have litchi automatically calculate the offset for all waypoints adjusting for my higher take off location ( ie one is done in mission hub but at the moment i am using the safer visual setting here due to the low margins for error)

Am i understanding this all correctly? For reasons that are irrelevant, i was hoping to be able to set one mission but work from multiple different take off points and elevations. its is too cumbersome if i am required to calculate an offset and then adjust each waypoint creating new missions for every take off possibility

 

[sar104]

Yes given circumstance i can navigate down to set my first waypoint at almost sea level take off , but for executing the full mission safely . I need to move to locate myself and TAKE OFF from a 25m higher elevation that is not above waypoint 1. This jacks the whole mission up 30m higher (where i was expecting online elevation to determine sea level and thus fly to my settings above that)

if i understand your comments correctly..
1) i should make calculations based on my takeoff position
2) set negative elevations for each waypoint to achieve my desired lower flight altitude and it will replicate the flight i had intended,.

Or am i misunderstanding and i can move to this higher elevation yet still set the mission to fly 5m AMSL based on some elevation data available that allows me to simply set my waypoint correctly? Thuis is entirely more desirable , as for reasons that are irrelevant, i was hoping to be able to set one mission but have multiple different take off points and elevations. Tjhis is too cumbersome for me if requiring offset calculation for based on each take off as a mission of mine can have 30 waypoints with a choreogrpahed changing elevation not easily allowing batch.

You are hugely overcomplicating it. Just ensure that the first waypoint is at your takeoff location. Then all the altitudes will be correct.

 

[TheDigitalDove]

You are hugely overcomplicating it. Just ensure that the first waypoint is at your takeoff location. Then all the altitudes will be correct.

And yes i appreciate that, but complicated as it may be , i am technically trying to understand how best to set mission to fly at elevation intended , where i need to take off from a remote location different to waypoint 1

 

[sar104]

And yes i appreciate that, but complicated as it may be , i am technically trying to understand how best to set mission to fly at elevation intended , where i need to take off from a remote location different to waypoint 1

Just create an extra waypoint #1 and move it to your takeoff location.