Very long (300km) corridor mapping project.

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To the collective brains trust. I've been approached by a colleague (licensed surveyor) to put an expression of interest in to provide an aerial survey of a proposed walking trail.

What is required is:
  • 10 meter wide corridor survey along the 300km route.
  • Accuracy is 50-100mm on the ground.
  • Cover 10km per day.
There will be a survey team placing GCPs along the route on the same day that I would be flying.

I've flown several sites to practice creating maps and I'm having reasonable success with the Pix4D app. I'm far from being an expert and yet to incorporate GCPs in my workflow but I have 3 months to get comfortable with using them to add the accuracy that I need.

My initial question is how many GCPs would be required to cover the daily 10km x 10m corridor to produce the 50-100mm accuracy my client needs. I'm also thinking that I could double the corridor width to 30m without too much extra processing time so that they can have more options to route the track.

I've also read that some mapping solutions are better for corridors than others. Recommendations would be greatly appreciated.

Many thanks in advance for answers to these questions..
 
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Double or triple the corridor?

Sound like a great gig...
It would be a great gig if it happens - very remote country.

I'm not pretending to be an expert in mapping yet so could you explain what you mean by double or triple?

If you're referring to the amount of passes, I'd anticipate at least three
 
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My company uses DroneDeploy and overall we are getting great mapping results. DroneDeploy has a flight planning mode called Linear Flight Plan, which is for mapping corridors, trails, streets, roads, etc. The attached image illustrates the Linear Flight Plan. The width of the course is adjustable.
 

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To the collective brains trust. I've been approached by a colleague (licensed surveyor) to put an expression of interest in to provide an aerial survey of a proposed walking trail.
How much tree cover is there on the route?
If it's all clear, no worries.
A few trees here or there isn't a big problem but if you run into more trees, that can make things difficult.

Here's a helpful into to using GCPs
What Are Ground Control Points (GCPs) and How Do I Use Them?
 
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Hi iClick,

Drone Deploy or Pix4DPlanner will work well for this purpose, but you will need to fly each section of corridor with at least two overlapping flight lines, three lines are better, so as the processing can create the stereo models needs for mapping.

To do this create your long flight plans (maybe max 1km long each) with, say, a 20m or 30m wide strip (the wider the better, within reason, even if your client only needs a narrower width). Set the sidelap to 85% or even 90%, so the s/w will create a flight plan that is narrow but will have at least 2 flight lines (again, 3 is preferred) for the image processing. You will get a result with 2 flight lines, but for accurate mapping purposes, 3 is much better.

Re the GCPs, it's tricky with such a narrow band of images, but I would suggest using post-flight GCPs, where you fly the area, inspect the imagery, then ground survey nice, clear, flat features (Eg painted road marking corners, concrete footpath corners, etc) in the imagery where the same ground feature appears in multiple images. This way you can input say 6-8 GCPs and if you need to add more to increase the accuracy, then you can do so easier than if you pre-mark the GCPs. Of course this assumes your corridor has good features...

You want to select GCP features that are as far apart as possible in width, but where they appear in 3+ images. Tricky with such a narrow corridor.

Hope this is useful!

Email me please if you would like to discuss further: [email protected]

Regards,
Dave
 
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We do corridor mapping for roadways. Map Pilot also has a linear mapping program that has been perfect for us.

The problems I see include the narrow width of 10 m. I agree that you must have at least 2 passes and we always do 3 passes at least. For right of way mapping we use GCP at 250' intervals and alternate between a centerline panel and two 75' offset panels, one on each side. For our needs, the elevations are critical to the design, so we use lots of GCP for the solution and check points. The output has been spectacular. But I believe that you need some wider GCP to control the inclined plane problems that can result from a narrow corridor flight.

I think 10 km per day might not be realistic. I fly 4000' segments with 500' of overlap on each end. This is optimal for one battery for each flight. For efficiency, I design the project to not require battery changes. I have done as many as 6 segments in a day but the light was getting bad. Remember that we really only have a 5 to 6 hour flight window where the sun is up high enough to cut down on shadows and give a good result.
 

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