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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    • Moderator

      Quan if you fly in South Africa and shortly all the SADC countries you better make sure you are legal. Jail time otherwise.http://www.safedrone.co.za/

    • @Gary,

      South Africa and Hobby Drone


    • Hi Gary

      Excluding South Africa, it takes about an hour to get clearance with the local Aviation Departments in the respective countries....we have been there and done it!



    • I didn't read the whole thread, just the first and last pages.  Try a few different types of software and see if that helps.  I use Pix4D, have tried Drone Deploy and AutoDesk ReCap 360 (limited to 250 photos).  Almost everything I put in now is geotagged (drone logs put into Geosetter).  All of these have a free trial for 30 days.  

      It does seem like you don't have enough overlap initially.  

    • Sure Gary - One of the reasons why we want to outsource the flying. It was fun but apart from the licensing issue, we would rather focus on the actionable insights - we are ag developer and manager, not drone surveyor.

      Thanks again for your advice earlier.

      Best, Quan

  • Hi Quan,

    Would be very much interested in discussing the opportunity of undertaking the Data Collection and Data Processing as per your requirement. We have gained a lot of experience in mapping large areas at a very rapid pace. We are using custom built UAVs with two hours endurance and can carry 1kg of payload. We are able to map upto 4400 Hectares area in a single day with 3.5cm/px for RGB and 10cm/px for Multispectral Camera. Plus the UAV being indigenous, we can get the work done in very affordable cost. The accuracy achieved by use of GCPs is upto 10cm. We are also working on the RTK systems to reduce the efforts of GCPs.

    Please contact me at pravinp404@gmail.com

    • Sounds great Pravin. 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  

  • There is a way for you to improve your UAV produced photomap precision significantly (cm accuracy level) without the need to use any GCP.  Check this link out. Or, you may try this for RTK GPS on your plane.

    • Thank you. We spoke to Walter before regarding our project. Our timing was too tight so we had to do it ourselves. Best. Quan

  • Hi Quan Le,

    I agree with the above comments. You need accurate ground control points if you are looking to produce an accurate model. The number and positioning and accuracy of the GCPs is also important and depends on the topography. This is something that comes with experience. Another aspect that hasn't been mentioned is image overlap. For consistent results, I would recommend a forward overlap of at least 80% and side lap of 75%. With a simple terrain you could probably get away with less, but rather safe than sorry. Their are other factors such as weather conditions, flying speed, camera settings that all come with experience.

    Having said that, you could probably get reasonable results from your images just by adding 5 or 6 well positioned ground control points.

    Let me know if you need any more info. You're welcome to contact me any time at ian@aerovision-sa.com.
    We are an aerial surveying and mapping company based in South Africa.

    Ian Freemantle
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