Dear all

We 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

Number of photos: 300-400

Photo taken out before processing: None

Software: Photoscan

Many thanks in advance!




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  • Hi Quan Le,

    I may be able to help you, my company has been doing precision Ag in the US and Ghana using the Sensefly eBee and other survey aircraft. We also work many software packages for post data processing, I would be happy to offer assistance. Please email me at

    • Hi Keneth thank you. We will. Best

  • Hi Qan Le,

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

    Maybe next time you can increase the overlap of images, i usually do 80% longitudinal and 65% lateral

    We are based in Cameroon and may help you for outsourcing, I sent you a friend request to discuss.


  • The second one is missing even more photos, so that's kind of a problem.

    I suspect you flew over the area of interest, you should have covered more of the surrounding area too.

    I too am surprised over the poor precision, also no elongated/stretched markings in the turns makes me believe you do not have a image skew (wrong picture matched with wrong position)

    - how did you match the position ?  - by CAM messages ? - why is so many photos missing ?  - and are all the rest of perfect, sharp quality ?

    hard to say anything more without the material. - but unless camera calibration if very off (like wrong lens), or geodata is mismatched with photos, I am afraid you can't fix it .   - maybe improve by setting manual markers in photos, but not fix properly.  The missing photos on leftmost part of second location will make that area impossible to stitch. (and calculate DEM at all.)

    • Hi Andre K 

      Thank you for your comments - I think they are valid e.g. we did have issue with geotaging. We could find the .tlog so we used Event30 geotagging utility. However there seems to be another geotagging activity with the log file on the Pixhawk autopilot - according to Event38 instruction manual. We couldn't do the second tagging because we couldn't get the log file from the using the microUSB cable. 

      I need to check with my team before I could respond more fully.

      In the mean time, would you be kind enough to repost your reply to this same post under "Agriculture UAVs"?

      I just moved the post to "Agriculture UAVs" as I thought it might be more appropriate.

      • Hi Quan,

        The Event38 Image Utility uses the CAM messages from the tlog in order to tag the images, so we do not run into the same problems typically seen by the time offset method, for instance.  The tlog uses its identification algorithm to match the CAM message with the appropriate image.  So even if you lose telemetry (and miss out on CAM messages) the utility will be able to determine the correct tags.  When comparing it to using dataflash logs, the only drawback is that you may miss out on a few geotaggs for your imagery.  But that tends to be a nonissue for most imagery processing solutions.  

        There are a few different renditions of the Event38 Image Utility, with important bug fixes.  Perhaps you have an aged version.  It would probably be a good idea to grab the latest.  As always, feel free to email me or Chris for help.  I am sure we will be able to get to the bottom of it. 

        • Hi Joe

          Yes we do need some help here. We also want to test out your drone data management software. I will email you separately. Best. Quan

      • Did not find the thread you mentioned.

        It sounds like you tagged from .tlog - that's a big no-no , the position is reported there with extra delay and/or jitter based on the telemetry link , at 10Hz.

        • Thank you Andre

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