Flight planning in difficult terrain

Hi – I have been flying IRIS+ for a few months, mainly to get an understanding of UAV’s as tools for environmental survey and monitoring as well as of course being cool exciting technology. As an ecologist and GIS user I am imagining lots of opportunities for working at the end of a RC transmitter. I have made many orthophotos that have proved the tools work and could be the basis for habitat classification etc.. I now have a definite task that I’m looking for some advice with.

I am involved with a coastal sheep grazing project in order to re-establish heath on what are currently bracken covered sea slope and cliffs. I hope to establish monitoring with both regular and IR photo monitoring. I would hope to repeat this twice yearly for at least 5 years with analysis done with a variety of GIS tools. I am just about finished in building the kit, just waiting for some photographic filters in the post. I am using a pair of identical Canon cameras running CHDK on a hard working IRIS+ drone.

Here is a link to the area I am working on - HERE - which is 1.5km of difficult to access north facing slope immediately adjacent to the sea. My plan is to have maybe 20 x 10m diameter areas that I make repeated very low level (high resolution) photographical + IR survey to monitor the change in vegetation composition.

The challenges are that my take off point is higher than the areas I want to survey so everything would require planning in negative altitude, the cliffs are very steep in places so may require altering the altitude whilst within the survey area and I am uncertain of the accuracy of the elevation information I have (taken from contour data). There are also the usual battery time issues so I would expect to be looking at maybe 5 independent flights.

Does anyone know about using absolute altitude (as opposed to relative) in flight planning and about the use of sonar in maintaining elevation? Would it be possible to rely on sonar to maintain constant 6m altitude in such terrain? Also do people have experience of adding missions together to perform complex missions where speed would vary dramatically eg 1.5m/s low altitude surveys over small areas then jumping at normal speed to the next survey site? I am hoping to achieve this without scripting if at all possible.

Twin camera mount:3691202968?profile=original3691202891?profile=original

Thanks in advance for your thoughts

David Tipping  

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    • I have some additional information.

      If you set the Verify Height while you define your WP, MP could define negative altitude.

      For that you need SRTM data which are normally downloaded by mission planner automatically.

      I did a test with Jersey island. Start the flight in the coast, move above the see and come back on the coast.


      3702792947?profile=originalBetween waypoint 4 and 9, the copter is above the see. We can see that there is no data from SRTM. We can see that Mission Planner defined WayPoint above the ground level (SRTM). 


    • I have been planning some missions recently where the launch point was about 200m above the lowest ground point.

      Mission planner seems to have some issues around this situation. When using the terrain data ("verify height" checked) and planning a grid at 50m above ground, I had to plan the grid, which turned up 50m above launch, send that to the plane to trigger terrain collection, and then re-plan the grid. After that the way point altitudes all looked pretty reasonable. MP seems to use some combination of SRTM data and google earth, which at 50m is good enough. There is an option on the planning screen right click menu under "map tools" to produce an elevation graph. This shows the Google earth heights, the SRTM heights and the way point heights. It's pretty obvious when its not right.

      When I tried to load them to the plane, any point that was less than the "Alt Warn" height above *launch* altitude was refused by mission planner. By planning the mission in absolute altitudes, and manually verifying that they all looked reasonable still, I was able to load them into the plane. Mission planner warned that it was unable to check them for me, but that's OK, because it was getting that wrong anyway.

      The other issue you might run into is that MP got quite confused when I tried to plan a mission for a remote location a couple of days in advance of travelling to fly the missions. It seemed, once again, to be confusing current altitude with mission area altitude. It seemed, under some circumstances, to assign local elevation to the remote home location. Seemed to be somewhat unreliable in this area and needed close supervision.

      Having said all that, arduplane did everything right on the day and even added altitude to avoid hills between waypoints. I still haven't worked out what value it is using for that separation distance. I suspect it is the "Alt Warn" value.

    • Thanks John - I think the answer is to get more height info by doing initial flights to gather data - see Pall Tamas reply further down. I have built a DEM from contour and point height data that i have done initial mission planning on. I translate this into negative altitude and it is ok but to improve this with actual point cloud info if i can work out how to do this would be awesome...

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