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:

Thanks in advance for your thoughts

David Tipping  

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Felix - do you know if it is possible to incorperate some mode or setting that maintains altitude based on sensor information eg the LIDAR-lite? What i would like is to define a mission in MP but maintain altitude over altering terrain??


David - I didn't try the LIDAR-Lite in auto mode yet (have as well a whole bunch of other things which I am planning to test), unfortunately we have very strong wind during the last few days. But I hope to get a chance this upcoming week and will report back.

That would be great - thanks

Hey Felix,

I can report success in getting LidarLite to work on my bench using the tips you provided.  Mission Planner had to be rebooted a few times for the connections to sort themselves out, but on the 3rd reboot (MP unplugged, UBEC unplugged, cold everything.) Wah Lah! I had 'Sonar Range'.

In testing I had the Pixhawk powered by USB hooked up to Mission Planner.  If I unplugged the UBEC (No Power to the rail), I was scolded with, "BAD Lidar health!"  So gettting 5v to/from the rail is critical.

I hypothesize the following results if a 35 degree forward tilt is used in mounting.

If I mounted at a 45 degree forward angle, and went backward for 45 degrees, the MR would drop to the ground.  Right?


Felix Hi - did you get to try Lidar-lite on a planned mission yet? if so did you use absolute or terrain setting in defining altitude???


Hi David - no, unfortunately I didn't have any time for outdoor tests yet.

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.

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.

Between 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). 


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