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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That would be a great application for the "follow me" mode!

Would it work in all modes?

it works for modes which keep/control the altitude of the copter (AltHold, Loiter, etc.)

Usually it uses the barometric pressure sensor for those modes - if you install a rangefinder sensor, then it uses the rangefinder up to the maximum distance which the sensor can measure (40 meter for the LidarLite, bit over 7 meter for a sonar sensor), if above it uses the barometric pressure sensor.


Neat. And looking at the spec sheet, <30g installed (+UBEC)? Anyone put one of these on an IRIS+? Perhaps use the front mount and still stay out of the way of the gimbal?


Multi Thanks!  I've been niggling at LidarLite for a few months.


Your video will help me get it completed.

1- I've got a UBEC to power LidarLite, and the resistors.  Using the UBEC to power the Pixhawk power rail, should I hook up the UBEC before or after the 3DR power module in order to keep noise down?  (My DiscoPro has open 5v power points that were used to power the Naza, but they're after the Power Module and I want to be sure to isolate the Lidar.)  

My ESCs are connected to the power rail, too. All 3 wires. Problem?

2- I'm probably going to mount the LidarLite at a forward angle, to give the MR time to react in fast forward flight. (Photos in the linked thread.)  Problem?

3- How is LidarLite going to function over water?  Smooth flat water that bounces a Lidar signal 45 degrees away into space?  (I'll test over a mirror.)

Again, thank you for the help.  Now I just need Lidar to work in 'Auto' mode.



1. Yes, you do have to provide 5V to the output rail of the Pixhawk, because the 5V coming from the Power Module are not connected to the output rail. You can use a ESC with built-in BEC or a standalone uBEC. I personally would not recommend to connect the 5V (red cable) of the ESCs if they have a built-in BEC, cause in this case you connect 4 (in the case of a quadcopter) independent BECs together. I have seen cases where ESCs did shut down because they did overheat (due to the BECs).

So, if you use a separate uBEC (that's what I personally prefer the most), then you remove all the 5V cables from the ESCs (only connect signal and ground). If you want to use the BEC of one of the ESCs, then leave the 5V connected from ONE ESC, and remove the red cable from the others (you can pull it out of the connector if you lift the small plastic clip securing it - afterwards make sure to insulate it to prevent any short circuit).

2. I was thinking of trying the same - but actually have doubts that it will deliver good results. You should keep in mind, that if you mount it with an angle, and fly backwards - then the sensor is pointed even more up, leading to false readings. Furthermore if you are in Loiter and have wind blowing from behind (so kind of flying backwards again), then the same happens.

I am actually going to test now, how much the angle of the copter (during flight) affects the readings and thereby performance of the sensor, cause a tilt of the vehicle (for example during forward flight) will tilt the sensor and therefore create a different range reading.

3. If the signal is reflected to the side (nothing coming back), then the sensor will not manage to read the distance. Have a look here:



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)

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.

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?


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...


I could be wrong about the landings in RTL for hillsides?  I filmed another one today and nudged it a bit (so it didn't RTL in the trees)  All was going well and out of nowhere it darted into the hillside & did the hoky poky.  It's darted off twice on me now on those tight landings, which makes me think the sats are blocked and a few feet off the ground it freaks. 

Maybe RTL to originally line it up and then full manual the rest of the way so that doesn't happen?  


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