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 would only use the terrain data as a rough guide.  The resolution is not good enough, particularly in Europe.  The best approach will be to fly numerous scouting missions to perfect the auto missions which you will save and re-run over the years.

    For your scouting missions, just fly in Loiter and note down on paper the altitudes shown on your TX at certain spots.  These will serve as altitudes when you plan your waypoints.  Eventually you will get a feel for the land yourself and be able to create very good auto missions.  Negative altitude waypoints will be fine.  You don't want to rely on above sea level altitudes.  Just remember to always take off from the same spot.

    I *think* in Tower you can now set your speed (and change speed) at way points.  This was not always the case - you had to manually set the waypoint nav speed parameter before each mission.  For you, you should be able to create a mission where you can set the speed between way points.  So in the end, all you will have to do is save a series of missions with altitudes and speeds.  Then re-run those missions each year whenever you like.

    There ARE sonar and optical flow accessories available directly from 3DR. However, unlike fixed wing (airplane) drones, I do not think there is any (easy) way to implement terrain hugging on the Iris+ or any of the quads.  You might want to inquire about that in one of the arducopter groups.

    • Thanks Erik

      I think you are right - basically itstrial and error to build a repeatable plan. I was hoping for a more elegant solution maybe following the ground with sonar or something like that. Good reminder to have a definate recorded take off site. I have contour data so will probably start there working it out mathematically in rough with plenty of slack on the altitude then note from the controller or maybe flight log.

      With one of THESE I could build up an accurate picture of the altitude but will have to wait till the price comes down.

      Many thanks for your advice


    • Hi David, 

      You are working with GIS. You need to make a vertical mapping of the area from a safe distance then load the pictures and log to a GIS software and do the DSM/pointcloud. That way you will have the altitudes down to the a few centimeter precision at each pixel. Then you can plan a closer flight.

      If you want to be 100% accurate you can make 2 mapping runs: one horizontal and one vertical. Both from safe distance. X reference the 2 datasets and you will be even more precise.

      If you want to take it further you can borrow some industrial grade GPS and add control points. 

      Just remember to add 2 meters to whatever altitude you want to fly at. (GPS HDOP on a bad day)

    • Hi - sorry i have not made reply but have been in France for 3 days. This sounds very interesting but beyond current knoledge, can we discuss this by email please?


    • Sure! 

    • Hi David, interesting camera set up, a couple of questions:
      1) How heavy is the load & what sort of flight times are you getting off the iris+ with this setup?
      2) You are using dual camera for what purpose? 

      p.s interesting works too..

    • It’s a work in progress at the moment. It clocks in at 445g which is heavier than I would like. Having spoken to 3DR they recommend that load carried should not exceed 75% throttle on hovering. This sits at around 78% on a still day. There are options for me to lose some weight, it was the principle I was developing and testing.

      The second camera is to be fitted with a filter that enables me to capture infrared light - see HERE

      As for flight times I don’t know yet as I’m still waiting for the bits to complete the camera conversion however I have flown a similar weight - a 420g bat detector and that gave me 12+ mins. I will post when I have it all working.

      I am using the IRIS+ to learn techniques and to see what is achievable. I will probably move to a larger frame with a bit more power and redundancy at some point.  

  • The height is relative. Where you take of from is ground zero. I have no idea if negative values can be input. I know that each waypoint can have it's own height. (Mission Planner, Tower) 

    • Here the result of my investigations:

      - mission planner 1.3.30 by default do not accept negative numbers for WP alt.

      - but if you go to the Flight Plan tab, there is a field called "Alt Warn" which is at 0. If you set it to -100 then you can set negative Alt to the WP ! (WP Alt >= Alt Warn). You can send it and read it back from STIL.

      - you can see the same WP values from MAVProxy command "wp list"

      - if you run a mission from WP1 at 40m and WP2 at -40m using STIL, you can see the copter doing the mission. It stop half way when Copter reach 0m. I don't know if this is an issue of the Copter Firmware or due to the fact that the SITL check the Alt and simulate the ground (need more investigations).

      Please don't take those conclusion as final conclusion for real flight as I just check with SITL.

    • To get ride of the ground simulation (issue for my tests) with SITL, I change a bit the SW.

      In ardupilot/libraries/SITL folder, I edited SIM_Aircraft.cpp. To the function:

      bool Aircraft::on_ground(const Vector3f &pos) const

      I forced the return to 0.

      Restarted SITL, injected WP with negative values and magic, it does the mission perfectly with positive and negative WP altitude.

      To be notice the land mode: visibly the land works but with only one phase not in 2 phases as it's below the 10m altitude. So the land Vz is very slow. If you want to land then set a WP close to the ground before landing.

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