Mapping mud banks

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TetleyK

• August 21, 2020 14:03

The boat club with whom I am a member has asked me to fly my drone over the upper tidal reaches of the river upon which the club is situated and to produce a map of the mud banks at low tide. These change on a regular basis and this map will allow the river to be more safely navigated by club members.

Flying the route and taking the photos is easy but stitching the resulting photos together to form a map is not so easy.

So, my question is would it be possible to use Reality Capture to do this? There would be a significant front lap but no side lap as there will only be one track along which the drone will fly. The UK Drone regulations restrict the corridor along which the drone can fly even though I have a PfCO from the CAA.

Thanks.

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  Erik Kubiňan CR

  • August 24, 2020 12:42

  Hello dear Mark, 
  very specific question I have to say. Although this might be rather possible. Good questions are,
  how fast would you be able to capture at least 3 frontal lines of pictures next to each other (you mentioned side would not be okay) of the river?
  Is the water calm and simply running or very rapid with some splashes and little waves going in it's movement?

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  TetleyK

  • August 24, 2020 13:12

  Hello Erik,

  The length of the section of river I have been asked to map is 9km. The drone will fly at 50m altitude and the speed at which it will fly (14kph) and the time lapse between each shot (5s) will give an overlap of 80% between each photo.

  At the time the photos will be taken it will be low tide and there will be very little water in the river and it will be smooth water and lot to mud.

  Thanks.

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  Erik Kubiňan CR

  • August 24, 2020 13:22

  Alright then, these are pretty good conditions for the success. The only risky one is the mud changing it's form as it lays down, but I think you should be able to manage that. What I recommend is to shoot in sections and every section of the length should have a line in the middle look straight down and then one from the left looking 45 degrees and one from right. Not exactly in the same line, but distanced of each other, just to provide the angles. This should do the job and the overlap you mentioned is very good.

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  TetleyK

  • August 24, 2020 13:41

  I will try this out on a short section of the river about 1km in length as take the photos as you suggest.

  Thank you for your help in this.

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  TetleyK

  • August 24, 2020 13:43

  A second question,

  If I only require a 2D orthographic map and not a 3D image, will the one nadir track be sufficient?

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  Erik Kubiňan CR

  • August 24, 2020 13:45

  It most likely won't. Process of photogrammetry is still used before the ortho can be created, so you have to treat it that way.

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  TetleyK

  • August 24, 2020 14:01

  Okay, thanks.

  Now, for the two side views, should the 45 degree camera angle point towards the centre of the river or forwards?

  I ask since a side angle is difficult to achieve with my drone.

  thanks.

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  Erik Kubiňan CR

  • August 24, 2020 14:20

  Towards the centre as that would mean you have the one spot, which is the point of interest, covered from both 90 and two 45 degree angles. Doesn't really have to be 45 but an angled view on what you already captured with the topdown.

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  TetleyK

  • August 24, 2020 14:31

  Many thanks, I'll try to find a way to get the angled shots.

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