How to mantain an altitude relative to ground level (partial solution)

[PeteM]

We all know that the flight altitude of our P4 is related to altitude of the takeoff point.

This means that if you start to fly from the base of an hill (always 0 altitude) and if you want to fly across that hill (for example altitude 100), if you set a cruising altitude of 50 you're going to crash halfway up the hill. You could set a flight altitude of 120 but, in a survey, this would mean having some photos (the ones taken at the beginning of flight) 120 meters away from the ground and some photos (the ones taken over the final part of the hill) at 20 meters above the ground... so bad...

The ideal solution would be to plan a flight that is maintained at a fixed distance from the ground, regardless of whether the terrain rises or falls... I searched a lot on the net until I found this video...

I did some tests and the concept works well.

Now the problem is how to link this concept to, for example, Mission Planner in order to manually adjust the altitudes of waypoints in a grid survey... or maybe to directly write a Litchi survey mission...

 

[Pharm]

That's how to do it. A few months ago, I shot a large piece of property using Litchi. One end of the property was about 50 ft higher so I set my waypoints higher at that end. Put it together with PTGui. Looks great.

 

[alokbhargava]

If you are working on mission hub, and on a larger screen, you will notice that litchi will provide you the elevation of each waypoint. You can use those values to increase/ decrease altitudes to maintain desired ground levels.


Sent from my iPhone using PhantomPilots

 

[r62ewa]

Although I have not tested the feature within the App, Map Pilot has a Terrain Aware feature so all of your captured imagery is consistent.

 

[PeteM]

After many hours of research and many failed attempts I found a procedure that satisfies me completely.

The procedure is based on the principle that the drone recognizes (one and only) the altitude measured from the point where it took off.

The first step is to import (from Google Earth into the CAD software) the raster map of the area to be mapped (only to have a reference map) and also the DTM of the area to be mapped (to have a rough idea of topography of the terrain to be flown over)

Once you got the DTM with MSL altitudes... you have to impose in that DTM that the point from which you take off is at altitude = 0 (and update the entire DTM based on this parameter)... now you will have a DTM referred to the point of take-off...

Finally, in planar view, you can draw the route of flight (according to your photogrammetric requirements) and then fit in height according to the DTM... this polyline will be imported in Litchi and everything will be ready for the mission on the field

 

[AlecW]

I read somewhere the other day that Litchi are working on an update to use terrain data to automate some of this. It was on the internet so must be true

 

[PeteM]

I read somewhere the other day that Litchi are working on an update to use terrain data to automate some of this. It was on the internet so must be true

Flying based on altitudes taken from Google DTM (or other global DTMs) is very dangerous.

As the drone (barometric) instrumentation only recognizes changes in elevation from the point of takeoff, I consider appropriate that all missions maintain this reference.

 

[GMack]

Trimble has a surveyor's drone (ZX5) where they claim an accuracy to within 8 inches. DJI would have a tough time trying to compete with that unless they fix their current altitude fluctuations against the German Trimble setup along with their software.

 

[AlecW]

Flying based on altitudes taken from Google DTM (or other global DTMs) is very dangerous.

As the drone (barometric) instrumentation only recognizes changes in elevation from the point of takeoff, I consider appropriate that all missions maintain this reference.

Could be they use known altitude to help set a consistent AGL set of waypoints to get you started. Obviously lots of variables like buildings so would just be a starting point to help setup a mission. Like I said, read on the internet so probably not true.

 

[Mallettron]

Maps made easy app has an addon that use terrain data, ideal for surveys. You can keep the height quite high so any errors wont result in crashing into a hill