We (www.gmxconsulting.co.uk) are developing a large-scale agriculture project in Nigeria (5,000ha) and started to use drones to survey and map topography.

The intention was then to use the Digital Elevation Model for irrigation planning and design. However, when we post processed the images we got very large x y z errors - please see the photos below.

1. Could anyone tell us where we have done wrong? Can we correct NOW (after the aerial survey)?

2. Also we look to outsource the drone surveying and post processing for our projects in Africa - Anyone interested please let us know.

Here are some more details:

Platform: E384

AGL: 120 - 180m 

Overlap: Front 60% Side 60%

GCPs: No

Flight time: <60 mins

Cameras: Canon S110 RGB and NGB

Number of photos: 300-400

Photo taken out before processing: None

Software: Photoscan

Many thanks in advance!




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    • Hi Darius we will reply with proper GCPs - There are still a lot area to cover.



    • Cedric, thanks for sharing. Excellent paper 

    • Thank you kindly sir!

  • This chanell https://www.youtube.com/channel/UCi1TC2fLRvgBQNe-T4dp8Eg/videos?ab_... can be usefull for you and this video after 10:00min https://www.youtube.com/watch?v=JJXwZiqe_Do&feature=youtu.be&am.... You can try identify point's coordinates from your data in existing map data and use them as GCP. As other have stated you need more overlap and GCP. Could also try to calibrate the camera with AGI PS and reprocess the images. I can recomend you to post this also at agisoft forum - http://www.agisoft.com/forum/index.php?board=7.0 RTK or PPK on the plane can  improve accuracy but ground control point's is a must IMHO

    Cyrill Stachniss
    Videos related to my teaching and research activities
    • Thank you for your advice. We think photogrammetry is a specialist skill that is best left to professionals. The flying was fun but we will look to fight people to work with on multiple projects. Best. Quan

    • Thank you.

      Execellent lectures by Cyrill.

      Any chance to get pdf version ?

  • Hi Qan Le,

    You can also try to recover your log file directly by extracting the memory card from Pixhawk and read it on your computer.

    Maybe next time you can increase the overlap of images, we usually do 80% longitudinal and 65% lateral. CGP will also greatly help. All said above already.

    We are a land / sea / aerial survey company based in Cameroon and Nigeria, and may help you for outsourcing, I sent you a friend request to discuss.


    • Hi Pascal

      Sure, we took the Pixhawk memory card with us back to London (the drone still in Nigeria). It's good to know that you near where we are. Let's talk.

      Best, Quan

  • Hi Quan,

    one question - the change in alt was during the flight?  if so way was it?

    it looks like this is the reason for the big elevation inaccuracy.

    if you have limitation to do the whole flight at 120m the do it in 180 the deference in the ground resolution is not that big of deference and I think that`s where the problem is located. we have done several vineyard mapping on topography called "running hills" whit no change of the altitude with grate successes 

    as for the GCPs you need it only if you want to "anchor" the orthopoto to the world if an accuracy of 2-3 m is OK you can use the UAV GPS.

    feel free to contact me by mail would love t help you with your project.

    have a great year




    • Hi Benny

      The first flight was at 180m and second at 120m AGL. They were entirely autonomous so I am not sure how the change in AGL affected the accuracy. Anyway for irrigation planning and we need accurate in the cm. It is actually not difficult for us to get a few GCPs. We just need to plan better next time.

      For UAV surveys the key outputs we need for irrigation planning and design are:

      - contour map with x y z at scale of 1:500

      - orthophoto

      As we are designing, developing and managing agriculture projects in Africa we would like to partner with UAV surveyor, companies or individuals. Our projects are generally >1000 ha. 

      Please could you send a proposal and some example of your work to quan.le@gmx.com ?



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