Linear Mapping Questions

Long time drone deploy user i have completed lots of regular mapping mission But this will be the first time i have to map a corridor.

The project in question is a 40km section of roadway with approximately 50 m on each side of the highway from center line that will need to be mapped. so 100m total width ±

all we need from this map is the edge of the trees on the existing clearing so we can survey a r/w for this roadway to lie in but the government wants to utilize the existing cleared space and not just go 50m from the centerline of the road. I figure it will be easier for us to map this and calculate the right of way using the orthophoto rather than send one of my survey crews out to survey in the edge of bush and c/l of roadway on both sides for 40km.

It will obviously need to be tie to ground control so we can insert it into our CAD drawing to find suitable locations for the boundary posts. realistically i only need this to be accurate to within 50cm or less. and i dont need super high resolution only to make sure we arent putting the right of way through the trees is all so i am planning on flying at 400ft

i am looking at the linear mapping APP and it looks perfect i only have a few questions.

  1. i have it planned for 3 runs, edge,CL road, Edge is that overkill? could i get away with 2? i am planning a trial run on a short 1km section before proceeding.

  2. Ground control - i was planning for 1 every KM painted on the roadway. would this suffice? Im thinking i may need more if i end up doing this in smaller sections…which brings me to my next question

  3. should i map this as one? right now its telling me 3500 images so its totally possible. But after doing some reading on here it seems people are breaking these corridors down into sections.

  4. How does drone deploy handle the elevation change? i have a 400ft drop from one end of the project to the other, which is not much over 40km. will the linear mapping APP hold a GPS altitude or will it still just go above ground level from the home point? which also brings me to my next question

  5. Home points - the fastest way to do this is to fly 40km one way, then back, then back etc however i would have to follow with the truck to manually land the drone once the batteries are low because the drone will want to return many KM back to home. Not really a fan of this method so im thinking this is why people are splitting these into smaller sections.

  6. Overall compiling…if i map this into say 3km segments, wwould a person compile all the images together if you overlap flight plans? because there will be an elevation change at each flight plan. will those compile ok?

Thanks for the help and any tips!

  1. Just run the left and right ROW, but just enough in that you get the roadway covered from both sides. As long as you are getting at least 70% front overlaps it will turn out well.
  2. You will want GCP’s every 1/2km, but space them so that you get overlap between the separate missions catching the same end GCP on each consecutive flight. Corridors need more GCP’s because of the linear nature and the fact that they are much more subject to twisting.
  3. I made a folder for the project and a project for each mile. If you are working in kilometers you might be able to do 2km/project as long as you are comfortable with VLOS.
  4. I don’t think Terrain Awareness works on linear missions yet so that is another good reason to break each 1-2km into separate projects.
  5. I don’t know what the regulations are for where you are at, but in the States VLOS is required and operating from a moving vehicle requires a waiver. This gets into a function that I have been asking of DroneDeploy @Andrew_Fraser since before they had linear flight. We need to be able to start and end a mission from a mid-point. I fly be the mile so starting at the 1/2-mile mark I should be able to have my 1st and last waypoints at the same area. This is the most efficient way with the ROW flight line method that I have been using. See this thread.
    Linear Mapping App
  6. If you are using GCP’s and the end GCP for each mission is included in the adjacent mission then your elevations will align. I again suggest having separate “projects” for each 2km segment. Once they are processed you can bring each 2km map into QGIS to create a master map.

I would highly recommend managing your final data in QGIS or some other GIS platform as they are designed to deal with data of this size. This will allow you to combine the orthos from all the flights with additional information like CAD linework and survey points.